Fabrik8

The only thing that could source power to that circuit (assuming that this is related to a component problem and not a shorted harness problem) with the switch unit removed, is possibly the idle speed control unit. I'd suggest unplugging that and testing the voltage to see what happens. This isn't to test whether the idle speed control unit is bad, it's just to get that part out of the equation to keep it from muddying the waters while you're testing things. The 8.3V is kind of a false positive I think, and I'm not going to confuse you by explaining why just yet.


I would still like to know what happens when you start with the switch unit jumpered and go from device to device to device down the chain and see where you stop getting 12V.

First of all, check the voltage at the switch unit connector when you have it jumpered.

If you see 12V at the switch unit connector when you have it jumpered (or 14V or whatever, it's the same thing):
You should see 12V at the input of the Evap Temp Reg switch, and 12V at the output (if it's working).
You should see 12V at the input of the Low Pressure Cutout switch, and 12V at the output (if it's working).
At some point in that chain of devices you will see 12V on one side of something and 8.3V on the other side. That's the important thing you're looking for.

I still think one of the two switches between the relay and the switch control assembly is not working.

marlinspike

Ok, I'll check those, but to be clear:
if I take the connector off the control unit and put a mutlimeter in 6 and 12 I get 12V (well 14, but like you said, 12). If I jump this, at the relay I get the same 8.3V that I always get, so jumping this isn't the solution. It seems like you understood that and so now I need to check the switches.

Fabrik8

Yes, check on either side of the switches and see what you come up with. I think you'll find that one of the switches isn't closed like it should be, so you'll get a different voltage on the input and output.

I could troubleshoot this soooo fast..

marlinspike

Ok, on the low pressure switch, I hooked up the red wire on my multi meter to the power side (with the connection connected to the switch) and the black wire to a chassis ground. 13.XV. Then I moved the black wire to the other side of the pressure switch...0V.

So the low pressure switch isn't closing I guess?

So I jumped the wires that normally go to the low pressure switch (turns on aux fan) and jumped the pins 30 and 87 on the relay side (engages clutch), and I didn't get cold air. So I guess after all this the pressure was low after all? But I still don't understand why leaving the relay in place and jumping the wires for the pressure switch only turns on the aux fan but not the compressor.

Fabrik8

You have 12V at term 30 of the relay, right? If you don't have 12V there, jumping 87 and 30 together still isn't going to engage the clutch.

marlinspike

Jumping 87 and 30 does in fact engage the clutch. However, it doesn't blow cold.

I've also noticed now that when sent to Economy (what a lot of cars call "vent"), even if set to blow cold, for some reason the upper side vents blow hot air (the rest of the vents blow unheated outside air as they should).

I think I'm going to admit defeat and go broke paying someone to fix this.

Archer

have you hooked up a set of guages to check your sys pressure?

marlinspike

Nope, don't have gauges, but I thought the fact that jumping the wires that go to the low pressure switch didn't engage the clutch ruled out that as the problem...I guess not.

Either way, trying to figure this out AND figure out why I now get hot air out of the top side vents when in the economy cooling mode (i.e. when everything should be blowing untreated air) is more than I can deal with. I give up.

The sad thing is, I had the heat out of 2 vents problem before, but I can't remember how I fixed it.

marlinspike

You know what...f it...a shop will charge me prob at least $160 in labor, and is extremely inconvenient...I'm just going to buy a push button unit, a rebuilt one is $140. I seem to remember that was the fix the last time I got heat out of two vents when everything else was blowing outside air (just looked at the monovalve and it's fine). A dealer tech friend told me if jumping the low pressure switch doesn't turn on the compressor and the relay works, it's always the push button unit. For all I know, when I jumped 6 and 12 I was jumping the wrong thing because the wire colors in my car don't match the wire colors in the book.

BAD4DR

Hey - Is your radiator fan for sure working?