The AC on my 1989 B2200 seems to be acting up. Around 20% of the time the AC light in the button does not light up and I can tell the compressor isn't trying to engage. Pressure in the system is fine and there's plenty of refrigerant because it's ice cold when it works. Fuses look good- I suspect a bad compressor relay but neither the owner's manual nor my haynes manual shows me where the relay is. Anyone know?

Thanks in advance,

-Nick

 

The relay is located behind the glovebox on the evap case. There is a thermostat there too as well as a blower resistor that can cause the a/c not to engage. Try jumping the 2 terminals on the thermostat. They go bad sometimes. There is a pressure switch on the reciever/drier that can be jumped to check it. If the compressor kicks in when the fan is in one speed but not others it is the blower resistor. I have never seen a bad relay but it is possible. I would start by checking for power at the compressor and working my way through the system. if you have power at the compressor the clutch is bad.

 

Cool, thanks! The AC working seems unrelated to fan speed, but I will monitor more closely. Follow up question: how do I remove the glovebox?

 

Just open it and you will see alot of phillips screws.

 

Soon after I bought my '88 B2200 in 1994, I also had intermittent AC (with both the compressor and the small light in the AC switch not operating). On mine, I traced it to an issue inside the switch itself; I pulled it out rearwards and was able to test it with just a test light, and it was iffy. Anyway, I took it apart and cleaned it out, re-assembled it, and it works fine to this day. So check that out first. If you need to go the relay route, the glove box comes out easily, as earlier poster stated; I know: I had to remove it to replace my AC evaporator about 5 years ago.

 

Thanks Cusser- that's definitely worth a shot.

Here's another symptom I noticed- if I cycle the fan switch on/off, I can get the AC to work if it's not responding to the switch. Any ideas?

 

The rotary fan switch must be ON, on one of the fan speeds, for the AC to engage. So maybe that's where your issue is. Next time it's NOT working, pull out that AC on/off switch, and see if you're getting any 12 volt + TO that switch. If so, then see if you're passing that 12 volt + though the switch when it's pushed in for "on". That should help isolate the intermittent, however, you must test that when it's not working.

 

Weirdly, the fan always works so I'm sure the switch is getting power.

 

Cusser,

What was the resolution to your AC issue. My 93 B2600i truck is doing the same thing. Cycling the on/off/speed switch would sometimes get the AC working. Now the switch trick doesn’t work. What fixed your AC?

Bob from Baltimore.

 

Bob - first question I ask is whether the fan speed always works in all four speeds; because the blower resistor can go bad, I've had this happen once. See this how-to:
Blower motor and blower resistor check out

The issue back in 1994 was that my AC push-in switch on the dash was intermittent. I pulled 6 of these from the parts yard a decade ago and found that 5 were bad !!! Wonder how many B-trucks here in Arizona were diagnosed as a bad compressor when just that switch was the reason. Anyway, here's a how-to for that AC switch, that could be your problem. One clue for this intermittent action should be if the little dim light in that switch itself is on when AC works and off when AC doesn't work - but that's tough to see, might need to look at that in dim light or night.
Repairing AC Push-in Dashboard Switch

I've never replaced the AC relay on the evaporator case.

One thing I have on my truck is a wire I soldered onto the AC clutch wire, which goes to a small light on my dashboard; that tells me whenever the AC clutch is actually getting power from the system, and should be engaged. One time that helped me diagnose a slipping clutch, which happened to get fixed merely by tightening the bolt in the center of the AC clutch !!!