My AC isn't working on my 96 Eddie Bauer 5.0L Explorer. Mechanically everything is fine. The problem is that there is no drive coming out of the EATC to activate the clutch on the compressor. Both the high and low switches are fine. I can probe the connector on the output of the EATC and drive the purple wire with 12v and the compressor clicks on and I get cold air. I have run the built in self test and got 888 back so it isn't showing any problem.

I was wondering if a bad cabin temp sensor could cause it to not turn on the AC? I am going to go to the heat setting and crank up the set point to see if the heater will turn on. Does anybody have any experience with this? Is there anything else I should check. I have the real Factory wiring/troubleshoot CD for 96, but it won't load on my Win7 laptop.

I'm an electrical engineer and was wondering if there is an output drive transistor that might be blown. Does anybody have schematics for the EATC internals?

 

So you're driving the purple wire at the back of the EATC, which would indicate that the pressure switches are closed and the PCM is at least not commanding the clutch relay to close (opening the circuit to the clutch). That would point to the EATC module or at least one of the sensors feeding it.

I have opened up an EATC module and don't recall seeing any relays in it, but that was also for a Lincoln LS with DATC. That being said, I don't recall hearing a relay close when A/C is requested so it is probably a solid state switch for the compressor relay. It would be easy enough to determine and, assuming you find a FET or BJT, test the component and also check for gate/base bias when A/C is requested.

Have you tried turning the temperature set point all the way to the coldest temperature and tried all the various vent configurations as well as the Defrost setting? I would expect that the Defrost setting will ignore the sunload and interior temperature sensors. However, all settings WOULD care about the ambient temperature sensor. If your ambient temp sensor is faulty it could make the PCM think the outside temperature is too low and prevent the compressor from engaging. That sensor though should be the same that provides the EXT temperature reading. Does that reading seem accurate? I'm not sure if it is an NTC or PTC thermistor.

-Rod

 

The outside temp gauge is reading correctly. I didn't try defrost...thanks for the tip.

My thought was that the cabin temp sensor was reading way low, causing the EATC to not turn on the AC. The self test checks that to a certain point. I found a replacement EATC at a local yard for $30. I guess I am just going to grab it and swap it in. I am working 11 hours a day and don't have time to screw with it.

Is the cabin temp mounted behind the little grill to the right of the radio on the dash?

 

[quote=oldmanXJ;Is the cabin temp mounted behind the little grill to the right of the radio on the dash?[/quote]

Yep, that's it. Some times there a little tube that guides air to another location where the thermistor actually resides. If you've done anything behind the dash recently you might want to make sure the tube is still connected (although behind the dash would likely be warmer than the cabin) and make sure the duct/sensor is not coated in a thick layer of dust and grime, especially if the vehicle has shuttled around a smoker.

-Rod

 

Thanks, I am going to pull the EATC tonight and do some probing and analysis to see if there is a blown transistor. I wish I had a schematic. I will try and take some pix and post them up here.