Hi, new member here, seeking advice!

Shortly after purchasing an '02 Expedition early this year, the EATC started pumping heat from the floor vents up front- and A/C from the overhead vents in back, when in "automatic" mode at a temp set for cooling. When placed on "Max Cool", it blew ice cold where it was supposed to. So, we just lived without the auto function and by the time it malfunctioned we had no more need for heat here in FL.

Fast forward to today.

Wife (her vehicle) calls as she's leaving work. Says she heard a "bang" shortly after starting the truck, before getting out of the parking lot, and then it started blowing hot air.

She gets home and I check all the relevant fuses and relay (swapped the relay out) and the compressor will not kick on. Worthwhile mentioning that up to today, never so much as a squeal, bark, or other noise that they usually make on their way out. Based on the "bang" she heard, I figured something in the compressor blew.

Decided to pick up a can of refrigerant for the heck of it, to see if I could get the compressor to kick in. While driving to the auto parts store, turned it on "max cool" to check it. It was then I realized that the "hot" air- was really hot air- as in, from the heater core. Normally, if a compressor isn't working it'll just be blowing outside air in- or so it is with every other vehicle I've owned.

It occurred to me that maybe, this is just another symptom of the already partially broken EATC system- though that doesn't explain the "bang" she heard....

Is it possible, that the EATC isn't calling for cooling as it used to, even in "max cool" mode- and that's why the compressor isn't kicking in?? Given that this system was already malfunctioning makes at least a little sense.

I have no idea how the EATC works- or how to troubleshoot this; to check to see if the compressor is being called on to work.

Thoughts or suggestions? You know what they say...if the wife ain't happy (and end of July in FL with no A/C will do that...)

EDIT:

Gets stranger...this morning found info on self-test for the EATC module- and it checked fine/no error codes. How can that be? As I mentioned at the beginning of the thread, there were issues shortly after purchase with the wrong temp air, coming from the wrong vents(!)

 

The way both analog and EATC systems work for vent contol is by directing engine vacuum to vacuum actuators (just like on a RX7's stock turbos) to open/close the doors inside the heater box. Temperature is controlled by the blend door actuator which operates very similar to a r/c car servo.

Analog systems use a resistor pack for fan speed control, while the EATC is pwm-based.

As for the rear, panel/floor selection and hot/cold is like a r/c car servo, while fan speed is resistor based.

I'd bet the blend door actuator failed. Mine is very dead too

 

The analog system uses a rotary vacuum valve switch, while the EATC opens and closes solenoid valves to achieve the same effect. In case of a failure, it defaults to defrost using outside fresh air.

Are you saying that when floor is selected that it opens the dash vents? They operate from the same actuator, but are opposite states. Vacuum applied equals floor vents open and no vacuum meand dashboard is open, or vise versa (i forget which it is). There is a halfway state triggered by a different line so both floor & dash vents are open too.

 

Travis,

Thank you for the replies. Haven't checked all the functions- but the key "puzzling" aspects remain as:

EATC self diagnosis throws no error codes- when I know the blend door isn't, and hasn't for months- functioned correctly. I thought the EATC checks the function of the actuators/blend door? Is that correct? Possible that the actuator is operating, but is not connected to the door somehow and therefore not "sensed" as a problem?

Before this event, it was obvious the blend door was not operating correctly in "automatic" mode, as it would put out heat on the front floor vents instead of the A/C which was correctly coming from the rear overhead vents. When switched from "auto", to "Max A/C", it would correctly divert air to the dash vents- and it would be cool air, and not heat.

But now, the compressor will not run, period. Is it possible that a defective actuator could somehow prevent the compressor/clutch from receiving power?

 

You're on the right track in terms of diagnosis. Just because the EATC sends the signal doesn't necessarily mean it is received properly by the designated actuator. Solenoids fail from wear over time and heat, anyone with a FD RX7 knows first hands how much of a PITA it is to diagnose turbo solenoid issues. Pump it up with a Mityvac, see if it holds vacuum (20inHg is fine) AND pressure (15psi should be fine). If they leak, replace them with new solenoids and retest.

A funky actuator can't knock jot the compressor. The rear actuators are completely electric too. Check for vacuum leaks on the plastic vacuum lines too.