Ford EATC (Electronic Automatic Temperature Control) Retrofit

Background:

The manual climate control system in my crown victoria was acceptable for short around town trips. But on longer highway trips, it was an annoyance to frequently have to adjust the middle temperature control and the rightmost blower motor speed knobs to maintain a suitable cabin temperature. Frequently adjustment of the climate knobs was also sometimes a source of argument with other passengers in the car who would make comments to the effect of "stop fiddling with the knobs, just leave them alone" and then a short while later comment "it's too hot" and then a little while later "it's too cold".

A climate control system that accepted the input of the desired cabin temperature and then automatically adjusted the vent discharge temperatures and blower motor speed would be convient and would also effectively elimate a source of friction with the other passengers in the car. Crown Victoria's in the LX trim level were avaliable with a feature called "Electronic Automatic Temperature Control" or "E.A.T.C." for short that accomplishes what we're interested in. Unfortunetly, EATC was not avaliable in the base civilian p73 or the police cruiser p71 trim levels. But it can be added if one is ambitious enough and has sufficent funds to purchase the needed parts.

Theory of Operation:

From a vehicle operator perspective, the HVAC (Heating / Ventilation / Air Conditioning) system in the crown vic is simple. With the manual controls, turn the right most knob to select which vents you want the air to be discharged from. Turn the middle knob to adjust the temperature. And turn the left most knob to control the volume of air flowing from the vents.

With the eatc system, press the automatic button and key in the numerical temperature that you desire (from 65 to 85 degrees) and then the system will automatically choose which vents to discharge the air from, how much air to move from the vents, and the required vent discharge temperature in order to maintain the vehicle cabin at the desrired temperature. Since the system is fully automatic, there is no need to continually adjust the knobs to maintain the same cabin temperature like you would with the manual climate control system. The eatc system also has manual overides for all of it's features, so on a damp day you can manually tell the system to direct the air towards the windshield. Or during the summer, you could manually tell the system to direct cooled air at your feet under the dash. Similarly, the blower speed can be overidden by turning a knob. And the automatic control of the vent discharge temperature can be overidden and set to full hot or full cold by setting the desired temperature to either 60 or 90 degrees. In this mode, all data from the interior and exterior temperature sensors is ignored by the control circuitry.

The inner workings of the system are a little bit more complicated though. There are two aluminum devices located inside plastic housings under the hood and under the dashboard. The first device is called an evaporator and directing air through this device cools the air and transfers the heat removed to the air conditioning condensor located in front of the radiator. The other device we're interested in is called the heater core, directing air through this device heats the air by transferring heat from the engine coolant to the air. To move the air through the evaporator and heater core, there is a motor with fan blades on a wheel attached to it called a blower motor. To control the temperature which comes out of the vents inside the car, a moveable obstruction called a blend door is located inside the air tunnels underneath the dashboard. In crown vics, air flows through the evaporator first and then through the heater core. When air is desired to be cooled, the blend door closes so that air will not flow past the heater core. When air is desired to be heated the door opens, so that air has to pass through the heater core before exiting through the dashboard vents. In crown vics, air always flows through the a/c evaporator even when the hvac vent discharge temperature setting is set to the full warm position. Although if the a/c compressor is not engaged, the a/c evaporator will not affect the temperature of the air. And similarly, if the engine has been sitting unused during a cold winter night, directing air through the heater core will not heat the air as the engine coolant will be at the same temperature as the outside air.

The door which blends the warmed and cooled air together is electrically controlled to give precise control over how much air passes through the heater core and the resulant vent discharge temperature. The doors which controls which vent(s) air is discharged from are controlled by engine vacuum.

Beginning the Project:

The first big step of this project is determining what is different between a vehicle with "climate control" and one with manual hvac controls.

The most obvious visual difference between the two systems is that the two control heads are different. But as noted below, numerous other support components are required to swap from manual controls to eatc ones or vice versa.
The vacuum harness which carries engine vacuum from the distribution block under the underhood windshield wiper mechanism to inside the car and from the harness junction near the wiper control module to the individual door motors is the same. But the vacuum harness which connects the junction block to the back of the control head is different.
The underhood evaporator housing is different because the manual blower motor resistor and the eatc blower speed controller that mount to the heater box are a different shape and size. The underhood evaporator portion of the the eatc heater box also has a fitting on it for the interior cabin temperature sensor. One solution to this problem would be to replace the manual evaporator housing with it's eatc counterpart. But if one has the proper tools, it is possible to modify the manual hvac evaporator box instead.
The heater air plenum located inside the car behind the dashboard is the same regardless of whether a crownvic is equipped with eatc or manual controls. But the blend door actuator mounted to the heater box is different.
The 14401 dashboard electrical harness is different between vehicles with eatc and ones without it. If you desire to add other civilian options to your police cruiser like a digital dash, autolamps, and the civilian clock and want the install to be "plug and play", then replacing your p71's dash harness with it's loaded p74's counterpart may be an attractive option. New 14401 dashboard electrical harnesses for recent crown vics carry a suggested retail of under $500 at the ford dealer. Salvage yard ones are asking for trouble as harnesses corrode when exposed to rain and snow, yards often cut the harnesses or break wiring when pulling other components and the harnesses are year specific. For instance, a 98' dashboard harness will likely work in a 99' with minimal complications but an 00' dash harness definetly will not work in an 01' without extensive modification.
The 14290 dash to headlamp electrical harness is also different between a police cruiser and it's eatc equipped civilian counterpart. The only difference that affects this project is that the police harness doesn't have the connector on it for the exterior air temperature sensor. This is a trivial complication that can easily be corrected with a little wire and the proper connector. Conviently, the 14290 harness in all recent crown vics has the mounting tab on it for the sensor where it crosses in front of the frame rail.
The 14a005 body electrical harness is the same between civilian crown vics with eatc and the ones without it. But police cruisers have their own unique body harness. Most p71 body harness will be wired for the eatc system, but you may run across one that isn't. But this harness is not a big concern as the only electrical signals for the climate control system that pass through this harness are for the blend door actuator. And replacment blend door actuator connectors with all 8 pins installed and a short length of wire attached are avaliable from ford for around $25.
Ford service part literature lists the dashboard trim peice surrounding the hvac controls as being different between vehicles with eatc and ones with manual controls. But all the hvac dashboard trim peices used in recent crown vics appear to accomodate the face of the eatc control head and have the castings in them for the interior temperature sensor.

A shopping list with applicable part numbers and pricing information for this project is avaliable here.

So in an oversimplified series of steps, to install eatc one has to:

Install additional sensors (Interior Temperature, Exterior Temperature, Sunload)
Replace the manual blower resistor with it's eatc speed controller counterpart
Modify the vehicle's electrical harnesses for the eatc system
Modify the vehicle vacuum distribution harness for the eatc system
Install the new eatc climate control head
Remove the dashboard and install eatc blend door actuator

Below are pictures of the old manual head and it's eatc counterpart.

Below is the back of the two climate control heads. Take note that neither the electrical connectors nor vacuum ports are the same between the two units.

There appears to be a common misconception among the general public that adding eatc to a ford vehicle equipped with manual climate controls is "plug and play". Some backyard mechanics have even gone so far as to purchase an eatc control head, only to find that it won't plug into their vehicle's dash harness.

Checking out the out manual climate control system:

A system which automatically combines cooled air conditioned air and warm heated air in precise amounts is going to be of little use if either the heater or a/c system aren't working properly. Similarly, if vacuum controlled doors inside the heater box aren't working properly with the old manual a/c system, they probably won't work right with the new eatc system.

So before beginning this project, we'll need a baseline to figure out if additional parts need to be ordered:

Turn the knobs on the front of the control unit and make sure that air gets discharged from the proper vents, if it doesn't you may need some new vacuum controlled door actuators or a new plenum assembly. A little bit of leakage to the floor when the controls are set to windshield defrost or dashboard a/c vents is acceptable. If air all the air always blows to the dashboard vents regardless of the position of the knobs, then look for disconnected vacuum hoses.
Flip the knob between a/c and max a/c and observe the recirculation door under the passenger's dash near the kick panel with a flashlight. You should see it open and close.
If the blower motor only works on "high" that's fine, as you're not going to use the old blower resistor or it's connector anyways. If you can't get any air to flow from the dashboard vents when you turn the knobs, that's a problem that you should correct before proceeding though.
Run the engine for a while to sufficently heat the coolant so the temperature guage on the instrument cluster is in the middle of it's travel range. Now set the control knob to a/c, fan speed on high and turn the temperature control knob between full hot and full cold. You should notice a change in the volume of air discharged from the vents as you turn the temperature knob since you're intermittenly forcing air through an obstruction to air flow called the heater core. And you should be able to get vent discharge temperatures on the full cold setting in the 40-45 degree range even on a 90 degree day in the summer. If not then the check refrigerant low & high side pressures, temperature deltas, and a/c compressor clutch cycling times to get an idea of the condition of the a/c system components and refrigerant charge level. If all is within spec, then disconnect the heater core hoses and temporarily install an inline coupler between the two hoses to bypass the heater core. If vent discharge temperatures are now within the desired range, the blend door is directing air through the heater core when it shouldn't likely due to the actuator. To check for sure, open the glovebox door and use a flashlight to look at the top of the actuator shaft, if it doesn't move when you turn the temperature control knob, you've confirmed that the blend door actuator is inoperative. A bad blend door actuator is not a problem as we'll be replacing it with it's eatc counterpart anyways, but this does prohibit us from knowing if the blend door itself is damaged or if an obstruction such as a pen or pencil is lodged in the plenum. Similarly, if you set the system to full hot and don't get hot air, watch the actuator shaft movement with a flashlight. And if there is a large temperature difference between the two heater core tubes, the core is clogged. And if you get a sweet smelling mist that's greenish in color out of the dashboard vents, you've got a leaking heater core. But a clogged or leaking heater core is fine, as it's not hard to replace once the dashboard is removed from the car anyways.

Adding Sensors:

Interior Temperature Sensor:

The interior temperature sensor is a resistive thermal device that converts temperature data into an electrical signal useable by the eatc control circuitry. More information on this sensor is avaliable by clicking here.

Exterior Air Temp Sensor:

Like the interior air temperature sensor, the exterior is a thermistor with a temperature dependant variable resistance. But unlike the interior air temperature sensor, no additional parts are required to prevent stangnant air from causing false readings as the sensor is in the air flow path of the radiator and condensor. More information on this sensor is avaliable by clicking here.

Sunload Sensor:

The sunload sensor is used by the eatc air conditioning system to determine when to recirculate the interior cabin air instead of pulling in air from the outside. Under normal circumstances, the sunload sensor has infinite resistance. But under bright light conditions, the sensor allows voltage to flow like a diode would.

In the pictures below, the sunload sensor is the one on the left. The sensor on the right is for the automatic light sensitive headlight (autolamp) system.

Blower Motor Speed Controller:

To be able to vary the volume of the air coming from the dashboard vents, the eatc controller has to be able to control the speed of the blower motor. This is accomplished by a relay, a darlington transistor, and some support components. The controller in question is mounted to the underhood evaporator housing which keeps the components cool since air going to the dashboard vents is constantly forced past it when the blower motor is turning. More information on the eatc speed controller is avaliable by clicking here.

Vehicles with the manual hvac controls use a conventional nichrome wire array to control the blower speed instead. While manufacturing costs of this unit are lower, it also only gives the vehicle operator 4 choices of speed while the eatc system in theory has an infinite number of blower speeds. Note that there are only 3 elements present in the picture below because "high speed" bypasses the resistor network all together. More pictures of this unit are avaliable here.

The eatc blower speed controller is physically larger than it's manual control counterpart which means that the evaporator housing could be modified to accept the eatc speed controller. But this task is easier said than done though as the engine blocks access to this area, as do the heater hoses & evaporative emissions components. But with a small dremel grinding wheel with a flexshaft attachment, it is possible to modify the housing with the engine in place by first removing the heater hoses and the evaporative emissions valve. The main points to watch for here are:

-that the transistor heatsink has adequate clearance from the plastic housing so that an adequate volume of air will flow by to cool the components and not cause them to fail prematurely or melt the evaporator housing

-the evaporator housing seals properly to the blower speed controller so that

water cannot damage the controller
air cannot escape and cause objectionable noises.
air cannot escape and reduce the volume flowing from the dashboard vents by diverting it into the engine bay
engine bay vapors cannot be vacuumed into the passenger compartment

Below are some pictures and sketches of the blower speed controller opening in the eatc evaporator housing.

Note that the sketches below are not to scale. Even if you plan on modifying the your housing, it is highly recommended to purchase a spare eatc evaporator housing to make your own pencil or crayon templates from.

Ford had only minimal modification of the plastic molding between the eatc and manual versions of the evaporator housings. This is convient because the thick raised portion of the evaporator housing that the mounting screws go into is setup for both eatc and manual versions of the car. So if one drills the holes for the eatc speed controller fasteners in the factory correct locations, the evaporator housing will have the needed strength to hold the fasteners in place without cracking.

Below is the manual evaporator housing in my interceptor. Take note of the three protrusions around the mounting hole that are not present on the eatc variant of the housing. Also note that the resistor opening is a different shape and the mounting holes are in different locations.

And here's the result after using a small rotary grinding tool and drill:

No need to cover the locations where the original fastener went as the eatc speed controller is large enough to cover them with it's insulating foam. It's also large enough to cover the spot where the rivet on the old manual nichrome resistor went.

To test if the hole was the proper size, I placed the actual eatc speed controller in the hole and attempted to slide it in all directions. This told me if the controller heatsink had adequate clearance from the plastic evaporator housing casting.

The method of rubbing a pencil on top of a plain peice of paper to make a template of the eatc speed controller hole proved to be very accurate. When I layed the eatc template over the manual hole, the fastener holes were drilled in the correct locations and the speed controller sealed to the housing without any noticeable leaks. This was especially evident when I removed the instrument panel and heater plenum from the vehicle and was able to visually observe the back of the evaporator housing.

Wiring:

To obtain the needed connectors and wiring and other support components for this project, I located a similar model year wrecked donor vehicle that had been involved in a rear impact collision. I then removed the dashboard from the wrecked eatc equipped 98' crown vic LX, seperated the wiring from the dash, layed the dashboard shell on the front seats of the car and purchased the 14401 dash wiring harness and evaporator housing. I then proceeded to bench test the components by plugging the eatc control head into the junkyard dash harness, and connecting the other climate control system support components including: sensors, blend door actuator, blower speed controller, and blower motor. I next applied power by connecting the negative terminal of a sealed lead acid battery to the grounding ring terminals and the positive terminal to the appropriate wires on the ignition switch socket and the constant live feed wires on the connectors that would be located above the blower motor and the brake booster. The climate control system was behaving as it should, the eatc control head powered up and displayed the temperature, turning the blower speed control knob controlled the blower speed, and adjusting the desired temperature caused the blend door actuator to move. The vacuum control block inside the climate control head was recieving +12V on the red wire, and pushing the different vent buttons on the front of the control head provided the appropriate pulsed ground signals. And to top everything off, the system passed the built-in self test documented here.

Now that I knew the eatc control head and other support components functioned properly, I had to decide how to procede. I could install the entire 14401 dash harness out of the wrecked LX into my police interceptor or seperate the eatc wiring out from the donor harness and add the eatc portion to my car. Some points to consider here included:

The junkyard harness was from a questionable source and is suspected to be corroded in places from exposure to the elements
I was not expierencing any odd electrical problems at the moment suspected to be caused by the dash harness
The donor dash harness was from the same model year vehicle as my police cruiser, so it would work with the rest of the electrical harnesses in my vehicle with minimal complications.
The harness was from a vehicle with a digital instrument cluster. Installing this harness would make installing a digital dash plug and play, but would mandate that the analog clsuter could no longer be used. I did have a spare digital dash around, but I'd prefer to keep my analog instrumentation at the moment.
Installing the donor harness would add autolamp automatic headlamp functionality to my police interceptor. But I already had autolamp functionality from a previous retrofit project.
The civilian harness would make installing the civilian dash mounted clock "plug and play". But would also remove the electrical connector for the trunk release button mounted in the middle of the dash. Not a concern either way as I am using the button in the middle of the dash for an alternate purpose and don't care about the civilian clock.
The civilian harness would disable the police power relay. But again, I'm not using the switched police power lead for anything anyways.
Installing a new dash harness would uninstall any car alarm and remote start system that was in the vehicle. Somewhat of a concern as reinstalling my remote start & alarm system would add additional labor to the project.
Removing the old dash harness from the dash shell and physically installing a new one will add labor while the dashboard is out of the car
Seperating the eatc portion of the dash harness would take time, but it would be under a relaxed enviroment when my car was not in peices. And installing the eatc wiring before removing the dashboard would better segment the project into smaller more manageable labor time allocations.
I'm comfortable working with automotive electrical projects and modifying my current dash harness for eatc functionality was feasible. But this is not the case with many people and installing a new $500 eatc dash harness from ford is probably the only way that some people will get their car working properly again.

Anyways, I decided to remove the eatc wiring of the dash harness and install just that portion of the harness into my police interceptor. Below is a chart of the wiring connections and where I connected the wires to my dash harness:

Connector	Wire Color	Where	Function	Notes

Grey Connector C227	Twisted Pair ([Pink/Light Blue] & [Tan/Orange])	Junction at obd2 diagnostic port near gas pedal	Multiplex SCP Bus for coolant temp & vehicle speed data	Instead of ghd seperate cold engine lockout (celo) switch used on antiquated crown vics, 1995+ ones recieve coolant temp data from the pcm via the data bus
Grey Connector C227	Light Green/Yellow	At drivers fuseblock	Constant +12V	Inititally was using the cigar lighter to power this wire but later moved the wire to a circuit because it's bad if the heater stops working if you plug in a defective cellphone charger or other accessory
Grey Connector C227	Purple/Orange	At driver's fuseblock	Switched +12V	A switched ignition +12V wire is present at the old manual hvac controls. But I already had a switched +12V wire connected to the proper circuit on the fuseblock from another project.
Grey Connector C227	Light Blue/Red	At Radio or LCM	Variable Voltage Dimming Output of LCM
Grey Connector C227	Black	At old manual hvac control head wiring	Ground
Grey Connector C227	Dark Purple	At old manual hvac control head	A/C low side cycling switch	Do not confuse this wire with the other purple wire that's used for the blend door actuator
Black Connector C228	Orange/Black	At old manual hvac control head or at cigar lighter plug	PWM Dimming output of LCM

Grey Connector C227	Pink/Black	Construct New Harness	Common sensor ground for interior air temp & sunload & exterior ambient air temp
Grey Connector C227	Blue/Orange	Construct New Harness	Exterior Air Temperature Feed (Underhood in front of horns)
Grey Connector C227	Brown	Construct New Harness	Sunload Sensor (Far passenger dash near a-pillar)
Black Connector C228	White/Orange	Construct New Harness	Interior Air Temperature Sensor (Near hvac vontrols)

Grey Connector C227	Yellow/Light Green	Yellow Light Green	Blend door actuator harness	You can catch the blend door actuator harness at the connectors where the body and dash harnesses meet under the glovebox. Or you can just run 5 new wires from the blend door actuator pigtail to the eatc control head.
Grey Connector C227	Red/Light Green	Dark Blue	Blend door actuator harness
Black Connector C228	Bright Purple (Below orange/black)	Purple/Orange	Blend door actuator harness	Do not confuse this wire with the other purple wire that's used for the a/c cycling switch.
Black Connector C228	Red/White	Red/White	Blend door actuator harness
Black Connector C228	Brown/Light Green	Gray	Blend door actuator harness

Black Connector C228	Light Green	To Blower Speed Controller	High speed relay	Applying +12V to this wire engages a relay inside the controller that provides a direct path to ground for the blower motor.
Black Connector C228	Yellow/Red	To Blower Speed Controller	Variable speed control signal	Do not apply +12V to this lead or you will damage the speed controller by burning traces off the circuit board. To test whether this portion of the controller works, apply +12V through an inline resistor somewhere in the 1k to 10k ohm range.
Black Connector C228	Light Blue/Orange	To Blower Speed Controller	Feedback signal	This output is connected through a 1k ohm resistor to the high current blower motor feed.

Black Connector C228	Red	Not Used	Digital dash english/metric switch	Installing a digital dash into my P71 would be trivial compared to adding eatc. But I prefer the feel of analog instrumentation at the moment.

Note that most recent ford vehicles share the same electrical connector housing for the eatc control head. But some such as older ford taurses have a very different pin assignment. Which means if you plug an eatc control head into the wrong vehicle, you risk permanetly damaging it. This is particulary troublesome as eatc control heads may be mislabelled at salvage yards and appear to be identical on the exterior.

Note: 98'-00' crown vic eatc control heads will not honor the requests for redundant steering wheel controls. If you think you may want to add steering wheel mounted controls for the fan speed & temperature later, get the 01'-02' revision of the eatc control head.

Note: It is assumed that the reader of this document is already familar with the operation principles of ford ccot (cycle clutch orifice tube) air conditioning systems. So the extent of coverage in this document of the underhood a/c pressure components is that if air is forced through the evaporator core and +12V is present at the purple feed wire on the low pressure cycling switch, then the air discharged inside the vehicle will be cooled and dehumidified.

Vacuum Distribution:

The vacuum harness part of this project was simple as the dash vacuum harness is seperated into two parts. The part that feeds the parking brake release and hvac system from the underhood vacuum distribution block is the same between vehicles with eatc and ones with manual controls. The part that is different easily disconnects from the other part of the harness under the back of the dashboard.

With eatc, the black vacuum hose is closed off to the outside enviroment when the engine is turned off. And all the vacuum actuators will rest at ambient air pressure which means that the outside recirc door will open and let the interior "breathe" when you park. With manual controls, an residual engine vacuum will still be applied to the doors and the interior won't be able to "breathe" if you leave your vehicle set on "max a/c".

Here's the two portions of the dash vacuum harness mated together. The big black rubber grommet is for where the harness passes through the firewall.

And here's the eatc portion that I need to swap into my manual a/c equipped car. If you somehow neglect to install the vacuum harness, all air flowing from the dashboard vents will come from the windshield defroster vents because the door actuators default to that position when no vacuum is applied to them.

And here's the two different vacuum connectors for the manual and eatc heads side by side. Note that they are a different shape and size, and also the vacuum hoses are layed out in a little different configuration.

Now that the wiring an other support components were installed, I installed the eatc control head and used it to control the blower speed and the vacuum controlled doors inside the heater box that control which dashboard vents air is discharged from. Until the old manual blend door actuator was replaced with it's eatc counterpart, the temperature of the air discharged from the vents was still controlled by the old rotary knob from the manual control head though. For testing purposes during this stage, I connected the new eatc blend door actuator and layed it on my center console. At first it was interesting to watch the actuator linkage move as the eatc system was trying to adjust the temperature, but after a couple weeks it became an annoyance and I became determined to finally finish the project by removing the dashboard and installing the actuator onto the heater plenum assembly.

Blend Door Actuator:

To regulate the interior vent discharge temperature, a moveable obstruction called a blend door is located inside the vent tunnels underneath the dashboard. When air is desired to be cooled, it is directed through the air conditioner evaporator core. When air is to be heated, it is directed through the heater core. To move the blend door, an electric actuator is used.

In the pictures below, the white actuator on the left labelled "MAN" is for vehicles with manual air conditioning. The black actuator on the right is for crown vics with eatc.

And here's the back of the actuators showing the linkage that connects to the actual blend door.

Here's the actuators at the other limit of their travel range.

And here's a picture of the actuator with the top cover removed. Visible are the drive gears, feedback resistor and motor.

Crown vics with manual and eatc both use the same heater plenum assembly, so an eatc actuator will bolt onto a plenum for a vehicle originally equipped with manual hvac controls. The problem is that to change the blend door actuator in a crown vic, the instrument panel (or in different terminology "dashboard") must first be removed from the vehicle which will take a few hours even for a skilled mechanic that has done the job before. And for the novice backyard mechanic, the job could well take a weekend or two.

For obvious reasons, do not install a used "pre-owned" blend door actuator. If you cannot afford to purchase a new $50 actuator from ford, live with your old manual controls until your finances improve. Blend door actuators are wear items and they are a big job to replace should they fail.

Since you're probably not going to be in a hurry to pull the dashboard again, consider replacing other wear items under the dash too:

Heater cores are wear items and are not difficult to replace when the dashboard is removed anyways. Typically, manufacturers design them with an 8-10 year life in mind, but they sometimes fail considerably sooner than that, but they also have been known to last in excess of 20 years without leaking. By murphy's law, if I didn't replace my 5 year old heater core when I removed the dash to replace the blend door actuator, I'd shortly after notice the classic signs of heater core failure, like a sweet smelling mist spewing from the dashboard vents, foggy windows, and getting an intoxicated feeling accompanied by a headache when driving with the windows closed. My core was not leaking when I inspected it after removal, but a new core was only $75 from the ford dealer and was cheap insurance against future problems.
The front upper door hinges have fasteners that are not accessible with the instrument panel in the car. If you notice that you have to pick the door up a little bit to get it to latch closed or you can see vertical movement of the hinges when you try to lift the door up and down, then you need new hinges and now is the time to install them.
If the previous owners of your vehicle drilled holes in the dashboard shell to mount microphones, radar guns, and other equipment and you want to replace the housing, now would be the time to do it. Or if you've got the stereotypical "rust free" southern vehicle with the "sunbaked interior" and a brittle cracked dashboard, now would be a good time to replace the dashboard. If you choose a used "pre-owned" dashboard from a wrecked vehicle as a replacement, watch that the metal isn't too rusty from being exposed to the elements.
The brake pedal switch wiring flexes a little bit each time the pedal is pushed. The wiring is more accessible with the dash out of the car, but then again replacing the brake pedal switch wiring pigtail is not too difficult of a job with the dash in the car. If you have an older car, or a car with a lot of stop-n-go driving and want to prevent complaints of "can't shift out of park", "stuck in park", or inoperative brake lamps then replacing the pigtail wouldn't be a bad idea.
Not a wear item, but if you want to install that full 1.5DIN radio and are going to swap out the defroster duct work, now would be time to do it.

An excerpt from the factory service manual documenting dashboard removal is avaliable by clicking here.

Notes about dash removal:

Disconnect the all wiring connectors for the dash harness both under the hood & inside the car. If you leave them connected and stretch the wires, you risk damaging the harnesses and causing some difficult and expensive to diagnose electrical problems.
You DO NOT have to discharge the air conditioning system refrigerant to remove the dashboard or plenum assembly. The a/c evaporator core is located under the hood not inside the vehicle like on most cars on the market today.
To remove the dash, you'll need to have both doors of the car open simaltenously. And you won't be able to close the doors them until you reinstall dash. So if you do work in a garage, it'll have to be a wide one.
Removing the dashboard from the vehicle can usually be accomplished by one person with decent upper body strength and flexibility. But installing the dashboard is a two person job.
You need to install the drivers side of the dashboard first, and the passenger side last. If you first put the passenger side on, you won't be able to get the dashboard shell over the large mounting stud on the drivers side.
Some people will find it advantageous to place each fastener in it's own individually labelled zip-lock bag. But if you've had the dashboard out of another crown vic recently, you can probably get away with placing all the fasteners in a single bag without labelling anything.
There are two fasteners on the drivers side of the dash. One is accessible by removing the lower kickpanel, the other becomes visible by removing the trim around the speedometer. You will need a 3/8" or 1/2" drive deep socket with a swivel extension to remove the upper one. Do not overlook the support that bolts from the steering column to the body of the car. Not remembering to remove the fastener will make dash removal very difficult. Forgetting to install this peice upon reinstallation of the dashboard will adversly affect the crash rating of your vehicle.
The transmission tunnel brace on the drivers side of the transmission tunnel can be removed by using a 1/4" drive ratchet.
The small bolt on above the kickpanel on the passenger's side can be removed using a 1/4" drive ratchet.
Older crown vics (~96 model year & prior) have an extra mounting brace to remove located the left of the glovebox door that will not be present in later vehicles.
The plenum assembly is held to the firewall using 4 11mm nuts. Three are easy to remove, the last on is located directly behind the blend door actuator. A flexible extension can get to the fastener. You could instead first remove the actuator and then use a conventional non-flexible extension instead. But removing the actuator is easier said than done. The front two fasteners come off easily with an 8mm socket. The back two are wedged underneath the windshield support though, so you'll need a small 12-point 8mm socket to remove them. But if you first take the plenum off the firewall, it's trivial to remove the blend door actuator.
The floor duct work that distributes heated air to the rear passenger foot well area prohibits removal of the heater plenum assembly. You can cut some slits in the duct work and later patch it back together to remove the heater plenum. Or you could remove the seats, floor covering, and air distribution duct work like I did. Removing the seats is a mixed blessing though as it does make some fasteners easier to access, but it also doesn't leave you anything other than the heard metal floor & transmission tunnel to rest the dashboard on. I happened to have around the big foam shipping material from an ATI LS1 ProCharger that worked well to support the dashboard though. And I finally got a chance to clean some stubborn stains off the lear rubber flooring in my car with some dawn dishwashing detergent and a garden hose.
Ford states that the pinch bolt on the steering column u-joint is a one use fastener. If you loosen it or remove it, you must replace it for safety reasons.
Don't forget to reconnect the heater core hoses before you start the engine
The factory installed spring loaded heater hose clamps often will not seal properly after you loosen them to remove the hoses from the heater core. So it's likely that you'll have to replace the factory clamps with some aftermarket worm drive clamps to prevent coolant leaks. Be careful not to tighten the worm clamps too much though as you risk damaging the aluminum heater core tubes.
The quick and dirty method mentioned on lincolnsonline.com of removing the bolts that hold the passenger side dash to the body of the car, then using a large prybar to bend the dash away, and holding the new blend door actuator to the plenum with just two bolts is not recommended and likely to cause problems later on.

Now it's time to put the dashboard back in the car and keep your fingers crossed that everything works right. In my case, the engine started up when the key was turned and I had gotten rid of an intermittent squeaking sound coming from the passenger's side of the dash. But I did have some odd electrical problems to contend with. The autolamp system sometimes wouldn't shut off the headlights and the abs indicator flickered on and off when driving over bumpy roads. Turns out the abs indicator feed to the instrument cluster shorted to the parking light feed which would intermittently give the abs bulb a ground path through the parking light filaments when the parking lights weren't on.

My first thought with the autolamp system was that I had somehow broken the wiring for the delayed exit rheostat. But since the headlamps would stay on for over 10 minutes, this definetly was not the case. I also noticed that the warning tone when the headlamps were on and the drivers door opened was disabled and the seatbelt buzzer was behaving oddly. Then noticed that my aftermarket car alarm system was intermittently sensing the ignition as "on" when it really wasn't. Could also watch the voltmeter on the instrument cluster jump up & the fuel guage move when the parking lights flashed on/off for car alarm event confirmations. Turns out that I had bad ground for the instrument cluster parking light bulbs, so when the parking lights were engaged it created a feedback loop telling the lighting computer that the ignition key was in the on position.

Anyways, after pulling the instrument cluster and running a couple new ground wires, and then disabling the old wiring the dash for the parking light & abs circuits and installing some new wiring, everything is working as it should. Fortunatetly, I did not damage the abs controller circuitry when the pulsed ground abs indicator bulb output was shorted to the +12V parking light feed. So have a copy of the evtm (electrical and vacuum troubleshooting manual) handy for your car before you pull the dash.

Using your new hvac system:

Well the first thing to do is to take a look at the owners manual section on operating the ford "climate control" system. Then run the self test documented here. If everythings checks out, make sure that air gets discharged from the proper vents when you press the buttons on the front of the control head. Now check that you can vary the speed by turning the control knob, and that adjusting the temperature setting varies the vent discharge temperature.

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