Repair info for the auto climate control module (EATC)

[sattech2000]

Looking to see if by chance there might be any repair info floating around for the automatic climate control modules in my 98 explorer and 2000 mountaineer. Both units won't turn on the ac and the blower motor is at hi or higher speeds.

I have a hot air workstation and capable of doing smt repairs, under a microscope if needed. Just need to information in these units to begin troubleshooting. Any ideas?

 

[J_C]

There are some topics about it, though you'd search for "EATC", or search for my username and transistor (link below). The most common fault is the firewall module, transistor fails. Some people call that a resistor module but the resistor based module is only used on the manual climate control, looks completely different with coils of wire instead of a heatsink the EATC version has.

Transistor itself isn't supposed to be user replaceable but it's just riveted and soldered on, or various brands still sell the whole module.

Search results for query: transistor

www.explorerforum.com

That doesn't cover the A/C though, could be a different problem.

There's probably a transistor in the head unit that drives the transistor module on the firewall, or something else could wrong with the head unit if the firewall module hasn't failed...another thing to check though you might find a head unit cheap at a junkyard. They aren't a common fault so I'd sooner get a used one than I would a used firewall module.

 

[sattech2000]

Doh....meant EATC, I have done some searching but havnt found anything specifically for repairing the control/display unit. I see people all over eBay offering the service so I cant imagine it's to difficult. I'll check out your links and specific suggested search terms to see what I come up with.

I did pull the module where the resister networks goes and didn't see anything out of the ordinary from a visual standpoint. I went ahead and resoldered all joints then reinstalled it. If I understood/remember correctly that is associated with the blower speed control but I could be completely wrong. Can anyone confirm or confirm what symptoms are associated with the typical failures of that module?

And yes, my ac clutch won't kick on unless I bypass the relay then it'll run all day but I know that not good because it won't cycle. Was hoping to repair the controller myself.

 

[J_C]

The firewall mounted speed controller may not have any visual signs of a fault. Typically the transistor fails. It can fall to a shorted state which results in the blower always running on high speed, but it can also fail to an open state where the blower doesn't run.

That transistor used to cost $10-13 but supply issues or inflation, now digikey wants $20 for it, might be cheaper elsewhere. The whole firewall module used to only cost $30-something (for an aftermarket brand instead of Motorcraft) but it may cost more now too. I found one at Rock Auto for $36:

More Information for WVE 4P1529

NPN 50A 60V TO3, part # MJ11028G

MJ11028G onsemi | Discrete Semiconductor Products | DigiKey

Order today, ships today. MJ11028G – Bipolar (BJT) Transistor NPN - Darlington 60 V 50 A 300 W Through Hole TO-204 (TO-3) from onsemi. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

There is probably a similar setup in the head unit, where the logic biases a much smaller transistor in the head unit, to provide the variable base drive for the firewall module, so whether that head unit transistor is getting power and outputting is where I'd start to probe it with a multimeter.

Look through the topic hits on the link I posted, one of those topics probably has the below attachment as well as more info, but here it is again, the 1999 Workshop Manual, Climate Control section PDF: