I have a 91 B2200 and I am trying to get my A/C to work. With the A/C button pushed in and the fan turned to the 1st notch the compressor clutch will engage but the fan does not blow any air. If I turn the fan switch to any of the faster speeds the fan works, but then the A/C compressor clutch dissengages and does not produce cold air.

one other thing. When you have the fan on the 1st fan speed notch with the A/C button pushed and the compressor clutch is engage the engine idles up and down to about 1500 rpm and back down to 800 rpm, just back and forth.

Any body have any ideas?

Is this a sign that it just needs re-charged or more than that?

 

It almost sound like the alternator isn't putting out enough to run every thing at once. When the compressor clutch is engaged, does the high side get hot and the low side cool off enough to produce sweat on the pipe? Have you tried jumping out the low pressure switch and turning up the fan?

 

I can check this today. Thanks

 

OK, I checked this, and found out that the Low side does start to get cool and the high side starts to get hot, however, the clutch won't stay engaged but for about 30 sec before it disengages.

 

Disregard my reply to your post on the other site. I was under the impression the clutch was being engaged the whole time. It sound like your little low on refrigerant. Pull the plug on the low pressure switch, use a paper clip to jump out the harness connector. If it stays on, you know what the problem is.

 

Thanks for the replies. The clutch disengages after about 20 to 30 secs of running, but only when the fan speed is on the 1st speed setting, if I turn the fan speed to any other speed setting the clutch will not engage at all and I noticed the little light on the A/C push button goes out when I change the speed setting of the fan to any speed other than the 1st speed setting.

So, that brings me to my next question, I know that when you "re-charge" the A/C system, you are supposed to turn all settings to A/C max during the re-charge, but doesn't the clutch have to be engage in order for the low pressure side to suck out the new refrigerant? If so I don't even see how I can re-charge the system on those settings if the clutch doesn't engage. Is it possible to recharge the system with it on the 1st speed setting when the clutch does engage?

One more stupid question, where is the plug to the low pressure switch and can you explain in a little more detail how to jump out the connector? I will check what you said to see if I can get it to engage.

 

I know exactly what the problem is. I had the same thing happen to my '90 B2600i. I have the shop manual with schematics, so I was able to figure out what would cause the problem before tearing things apart.

You need to replace the Fan Speed Resistor! You pull out the glove box, and behind that there is a unit that is screwed onto the air duct called the "resistor assembly". You remove the wiring connector and remove the two screws holding it in and there will be a break in one of the resistor loops.

It cost me $35 or so to buy the unit from the dealer, and about 15 minutes to put it in. Problem solved. Of course, mine broke on the hottest day of the year two years ago.
Good luck!

 

Um, OK this does sound like it has something to do with the fan speed control. Thanks, I will definately check this out.

 

It sounds odd I know. The reason the compressor won't stay running is because there is no airflow through the evaporator without the fan running. The pressure builds up and it goes out on high pressure. There always has to be airflow through the evaporator, which is why the AC unit won't turn on unless the fan is on.

If you look at the schematic, you'll see that the AC unit is tied directly to the fan control to make sure it goes off when the fan switch is off. When the switch is in Low, the AC unit runs, but the fan does not. When the switch is in medium or high, the fan runs but the AC unit doesn't, right? Exactly what mine did. Resistor Assembly guaranteed.

 

That is "EXACTLY" what mine is doing. With the exception of the abnormal idle when the A/C clutch is engage. But I think that maybe a seperate problem, because I traced the abnormal idle to the vacuum switch that goes to the diaphram by the throtle on the carb, that controls the idle up speed when the A/C is on. With the vacuum switch unpluged the clutch will still engage however the idle is dropped way low.

Any ideas on that? Do you think it is the vacuum switch or the diaphram by the carb or other?

Thanks again.