K Brockschmidt

I've moved the AC system from a 94 del sol into my 93. The mechanic I'm working with has leak tested and charged the system, and applying power to the compressor and such gets everything to run and blow cold.

However, the switch on the dash isn't working to turn the AC on, and we're wondering where to look for the problem.

When I transplanted the system, my 93 wiring harness had the 2-wire plug, so I spliced in the 3-prong plug from the 94. I didn't splice in the black-yellow wire from the evaporator thermostat at first, so perhaps that's the problem. We did apply power to it, but that didn't seem to help make the switch work.

I'm wondering if there are other parts that might be bad, perhaps the relay that's attached to the evaporator unit under the dash? Has anyone made this kind of transplant and found that the 3-wire thermostat needs to be wired in a certain way?

deschlong

iTrader: (8)

3-wire thermostat is powered, I believe (vs. a more passive one in 2-wire), so it needs the third wire. Connect it to the BLK/YEL in the loom there ... use a quick-splice if you don't want to solder.

K Brockschmidt

Thanks. I've hooked that black/yellow wire up and confirmed that it has 12v on it. Compressor still doesn't come on though.

Looks like I have some troubleshooting to do using the flowchart in the service manual. Perhaps the thermostat is bad, although the yellow/white wire seemed to have 12v on it. That leaves the possibility of a bad pressure switch or something wrong in the ECM.

The compressor clutch relay should be good as it's new.

But if there's something obvious I should try first, let me know.

deschlong

iTrader: (8)

For sure, follow that troubleshooting first and foremost.

K Brockschmidt

Looks like the switch or the blue/red wire from the switch is open. It's supposed to go to ground when the switch is on, but that wire isn't. Manually clipping that wire to ground turns the whole system on just fine, so next step is following the wiring harness back to the control module to see what's up.

K Brockschmidt

Found the problem. Tracing the blue/red wire back to the heater control module showed that the wiring is intact. I then removed the control module to test the output pins, and the connection wasn't happening with the switch.

I took the control module apart, which is fairly easy to do by removing a couple of screws and unhooking the plastic tabs. There I found that a trace on the small A/C switch circuit board was broken! It almost looks like a manufacturing defect, perhaps the trace was broken when the unit was first assembled.

Normally one would replace this whole module, but it was a simple matter to solder in a jumper to bypass the break. One note: although it's temping to route the jumper through the U-shaped opening in the board, don't: this is where the switch cover on the outside of the module comes down.

Anyway, putting in the jumper and reassembling everything has the switch working properly to turn on the A/C system.

deschlong

iTrader: (8)

Beautiful!! As much as tracing electrical gremlins is annoying, it's pretty gratifying when it works out. Especially when it wasn't your fault to begin with (ie., a mistake with the install). And .. wow that board was rekt.