A/C Electrical Issues

[richduck]

Symptom: Compressor will not engage, switch lights up and blower switch works.

Checked all fuses, not just visually, with a meter, went through diagnostics and the fan motors come on when connecting the Bu wire at the diode to ground, compressor engages when connection diode Bu/R wire. FSM says I have a open in the Bu/R wire.
I also show open at the switch connector Bu/R wire and at the Delay Control Unit R/Bu wire.
Diodes and relays all test good. The cooling fan relay connections in the under hood fuse box are a little strange though. I get 12v through the 1-2 circuit but I have no voltage on either side of the 3-4 circuit that should get switched when power is applied to 1-2. Seems like I am not getting power to the circuit I can't find the open and I am running out of places to look. There has been no aftermarket goodies added, there have been no splices or hack wiring done to the car and everything else electrical works like a champ. Anybody have any ideas where to look next?

[2drSE-i]

I know you said you checked the fuses, but did you check the rear defrost fuse? I chased electrical demons for around 2 months last summer and it turned out to be a popped rear defrost fuse. It supplies power to the compressor clutch.

[richduck]

Yeah I did, I read that thread as part of my diagnosis. During my testing I popped that fuse and lost the lights to my control buttons.

[Dr_Snooz]

You've definitely done your homework, but have you checked your freon level?

[2drSE-i]

You've definitely done your homework, but have you checked your freon level?

The pressure switch is the first part of the diagnostics in the shop manual. He should have done this as well. Must have a break somewhere.

[Hauntd ca3]

find the low and the high pressure switches, disconnect on at a time and bridge them out with a bit of wire and see if the compressor engages.
with the age of these cars they are usually low on gas and need a recharge.
bridge out the low pressure switch first and if the comp engages, time for a regas.

[richduck]

Pressure switch was first on the list, gas levels are OK as well. I can run a hot wire to the comp and it will engage. Seems like I am not getting power at the start of the circuit but I am not sure where the circuit actually begins! Almost seems like there are two power feeds for the AC system and I am not getting power to one side of things. Has to be a break somewhere but the way these systems are joined with others you'd think another system would be affected as well, but that is not the case.

[Pnem3]

Have you checked the thermal switch on the evap that keeps it from freezing? It is easy to overlook. Just bypass it by putting a piece of wire between the terminals.

[richduck]

Checked the wires for voltage and got nothing, but I'll try the bypass.

[Pnem3]

How about the switch on the dash? The fan switch plays a part too.

[Dr_Snooz]

When and how did this start?

[richduck]

Dr_Snooz:

Started when I dropped my son off at practice. Had AC on when I took him and turned the car off to talk to the coach. Left 5 minutes later and the AC hasn't worked since. Been fighting this off and on for almost 2 years! And yes, I start the diagnosis from the start each time, just because it checked OK once doesn't always mean it stays good. I know I have an open or a bad something but I can't seem to track it down. My 240Z is much easier to diagnose and repair.

[Dr_Snooz]

It might be worth purchasing the factory manual from helminc.com. There are big foldout wiring diagrams that I suspect would be enormously helpful in your case. They are too big to scan or I would have already.

Also, I'm not sure if you have looked at it already or not, but the Electrical Troubleshooting Manual on the wiki might be more useful than the regular manual. It's for the '89 model year, but there shouldn't be any difference from '88. I'm not sure if you noticed any hot wire smells or anything when it happened, but anything you can remember might also help.