Hi Guys,

I've found a few discussions related to a lack of current at the A/C compressor but I'm still stuck trying to diagnose the problem with my Gen I.

1990 Montero LS 4D

I had the A/C recharged a few weeks ago and everything seemed to work fine. A week later I turned it on for the first time while driving on a hot day and got nothing. I am not getting any current at the compressor or the fan and can't figure out where the problem is. The blower seems to be getting current and both fuses behind the glove box are good and have current flowing through them. I thought it might be the push-button switch so I replaced it and the situation is the same.

I think that the problem is between the battery and the switch and not between the switch and the compressor. Please correct me here if I'm wrong. In order for the switch to work the blower must be on. On the switch itself, current enters via a green wire with a white stripe and heads out to the compressor via a black wire with a white stripe. As far as I can tell, the green wire has no current and I have checked it at numerous spots under the left side of the dash.

So here are a few questions:

1. Am I misunderstanding the role of the wiring at the switch and the need for current in green wire with the white stripe?

2. I though it could be an AC Compressor relay that is bad and I found one to order online. But where is it located on the truck?

3. Could this be a problem with the dual pressure switch? Where is that located?

4. There is a switch that is connected to my A/C vacuum hoses. What is this? I get current on one side of it but only very faint current on the other side. I can replace it but I don't know what it's called.

5. Does anyone have a diagram for this that includes the colors of the wires?


I've gotta get this fixed; it's HOT here in DC! Plus I'm driving back to LA in two weeks.

Thanks for your help,

Matt

I'm thinking now that the green wire with white stripe at the A/C on/off switch is for the light that illuminates the switch when the headlights are on and may not be related at all to the black wire with white stripe that travels to the compressor.

Thoughts?

Couple of things...First run a 12V pos lead directly from the battery to the plug @ the compressor to verify that the clutch is good to go. You should hear it engage. Plug it back in. Once you've done that, got to the pressure switch located near the condenser on the passengers side. Unplug it, then bypass it by inserting a paperclip into the end of the plug. If your compressor engages now, that means one of two things bad switch or lack of pressure in the system. My bet is a leak let out the pressure and now the switch is doing its job and not letting compressor turn on. If Both these tests check out, then check the temp switch near the thermostat, this will turn off the AC when the engine temp gets too hot. It could possibly go bad too.

There is an A/C relay to also be considered and.... the temp switch on the water box signals a relay inside the ECU that in turn sends a signal to power the clutch. The compressor power switching is fairly complicated.

Frank

I was sitting on a job site one day watching concrete dry, and started listing out the current path for the a/c. It is more than complex. I had 4 columns on an 8.5x14 pad, and I was about half thru.

I'd follow Justice's advice above. It's what I'd check. My bet is that it leaked out and the low pressure switch is killing the compressor.

One of my Raiders developed an annoying tendency of not wanting to turn the compressor on until the truck was good and warmed up. That was a bad thing when it happened here in Phoenix, where having the a/c on and functional is almost considered a need at 6 a.m. when it's 95 degrees (F) and seems to climb by the minute.

I never was smart enough to figure that one out, and even less smart for not asking on here. In my case, the temp sensor wasn't it, nor was it the pressure sensor/cut-off thing. It would turn on after a few blocks, then run perfectly after that, cycling just fine.

I wish you luck in fixing this. It's great when they work right, too, as all my Monteros/Raiders have practically made my hands numb from the cold air blowing around the steering wheel (i.e., they work very well).

John B.

In my 91, after extensive troubleshooting, I eliminated the ECU from the circuit. It's been good to go ever since. Everything functions as normal to include the thermostat, but I suspect the overheat shutoff function probably would not. I hope I'm smart enough to turn it off myself if I start to overheat.

Hey guys,

Thanks a lot for your help. It looks like everything was doing it's proper job since I discovered that I have absolutely no pressure in the system. When I got the system recharged the mechanics told me that they found only one tiny leak that only leaked when the system was on so I just figured that the system was still charged since I hadn't run it at all between the time when it was charged and a week later when I tried it again. And you know what they say about assumptions.

I haven't been able to find any leaks so I'll take it back to the mechanic and see if they can find any repairable leaks.

If they find out anything useful, I'll post it.

Thanks again,
Matt