AC Question

[Mike Feinstein]

My AC system is fully charged and working great....most of the time. For some reason...usually when I need it most, the system won't work. The fan blows just fine and usually blows ice cold air. But, once in a while it simply blows outside air even with the temp switch turned to the coldest setting (this is July in Georgia). Here's my question:

What would cause the system to turn off the compressor prematurely? There must be a temp sensor somewhere that turns it off when the car reaches the desired temp. Could it be the temp switch/capillary tube? Do they go bad? Is there a sensor somewhere that is acting up?

I've replaced the fuse and the AC relay in the smugglers box but it didn't solve this intermittent problem.

Thanks for your help.

[Jim Sims]

Does your compressor output (between compressor and condenser) have a pressure switch installed? Does the system shutdown when its very hot outside and you are creeping along in traffic?

[Jadams1]

I agree with Jim, most likely high head pressure switch is holding out the compressor clutch.

[Don Wohlfarth]

I'm not sure you have a high pressure cut out on your system. Guess someone could have added one.
You might want to check the wiring at the cabin thermostat as it runs directly to the a/c clutch. I had a loose terminal at the stat and it would not always allow current to pass to the clutch.

[ruf-porsche]

Originally posted by Mike Feinstein
My AC system is fully charged and working great....most of the time. For some reason...usually when I need it most, the system won't work. The fan blows just fine and usually blows ice cold air. But, once in a while it simply blows outside air even with the temp switch turned to the coldest setting (this is July in Georgia). Here's my question:

What would cause the system to turn off the compressor prematurely? There must be a temp sensor somewhere that turns it off when the car reaches the desired temp. Could it be the temp switch/capillary tube? Do they go bad? Is there a sensor somewhere that is acting up?

I've replaced the fuse and the AC relay in the smugglers box but it didn't solve this intermittent problem.

Thanks for your help.

Yep the temp switch / capillary tube cycle the compressor on and off. The capillary tube may have leak out all it freon or may not be inserted in the evaporator correctly or may just be dirty and needs a cleaning with a crocus cloth (don't use emery cloth).

[Mike Feinstein]

Thanks guys. I'm sure the system is stock so I don't believe a pressure switch has been added.

Jim, yes...the problem seems to occur when the car is hot...like when it's been in the hot sun for a couple hours before driving, or when it's extremely hot outside...what does that tell you?

I removed the brass colored end of the capillary tube from the evaporator and cleaned it with a small piece of 2000 grit wet/dry sandpaper. It didn't look very dirty and appears to be dry and sealed so I reinserted it all the way and will hope for the best. Of course I could not examine the entire length of the line as it is insulated. It seems to just rest in the evap opening without any clips to hold it in place...hmmmm, but doesn't seem to be going anywhere. I added a small tie wrap just to be sure.

Thanks,

[scottb]

When did you last have your system charged? Is it possible it was overcharged, causing high pressures? Or, if you have non-barrier hoses, is it possible the charge is too low, and somehow on really hot days the system goes into "meltdown?" I'm an a/c newbie, so if my comments are off-base, guys, please don't flame me!

Cheers.

[ruf-porsche]

Originally posted by Mike Feinstein
Thanks guys.
I removed the brass colored end of the capillary tube from the evaporator and cleaned it with a small piece of 2000 grit wet/dry sandpaper. It didn't look very dirty and appears to be dry and sealed so I reinserted it all the way and will hope for the best. Of course I could not examine the entire length of the line as it is insulated. It seems to just rest in the evap opening without any clips to hold it in place...hmmmm, but doesn't seem to be going anywhere. I added a small tie wrap just to be sure.

Thanks,

The capillary tube should be inserted into the fins of the evaporator. When the evaporator is warm the heat is transferred to the capillary tube which cycle the compressor to turn on. When the evaporator is cold, the capillary tube is also cold so it will cycle the compressor off. You need to cycle the compressor off so that the evaporator doesn't freeze up.

[david914]

OK, this is very simplistic, but have you checked the spade connector at the pigtail from the clutch to the body harness? Years ago, mine was doing the same thing and I checked this connection and it was not good resulting in a melted connector and wire. Might be worth a quick look.