A/C Issues

[swampslider]

96 Tahoe. The A/C works fine in 80 deg. Weather. At 94 and up, it will work as long as your moving but heats up if your sitting for a 15 to 20 min. period. Also if you shut everything down for 30 min. The clutch will not come on. I replaced the High pressure switch but it still wont engage. it will remain that way for hours till it cools off completely. The low pressure line is as hot as the high pressure line
This morning I put a cheap gauge on the low pressure side. At start up it was at 25 psi and rose to 35 psi after 1-2 min. At this point I revved the engine the pressure dropped below 15 psi and the clutch disengage. After returning to idle the clutch reengaged after 3-4 seconds. When idling the cab temperature from the vent was 40 degrees.
Any ideas on what could cause this.
Thanks in advance for any input.

 

[SunlitComet]

first it sounds like the fan clutch is slipping. Maybe as far as the clutch cycling you really need a full set with high and low gauge. You can learn so much more. one side just don't cut it. based on what you mentioned it sounds like blockage in the system but the gauge set will help tell.

 

[ezdaar]

If it blows colder when moving. The fins on the cooler in front bumper are clogged up and or your clutch fan is no longer working as intended and not pulling enough air through.


This is when most people swap to electric fans as they pull Alot more air at idle than the clutch fan does. it solves 99% of everyone's warm air at idle problem.

 

[swampslider]

I took it to an A/C tech friend. He checked the pressures and said they were right on. Needed a little coolant to bring it up to par. I'm gonna check the fan clutch tomorrow. We checked the condenser and it is clean. Pulled the control module out and found two sets of wires that were on the bottom that were loose. I pushed them in about 3/8 of an inch. Have to wait till tomorrow when its hot to see if theirs any change.
Thanks for the responses and suggestions guys.

 

[SunlitComet]

you have pressure readings with outside ambient temp and humidity reading. as well as the same inside the cab?

 

[swampslider]

I didnt wright them down. Outside temp was around 87, Low side was around 39 psi and the high side was around 220 if I remember right. Humidity was around 80 percent. Cab temp was around 40 deg from the duct.

 

[swampslider]

Ok, Changed out the clutch fan, it was weak. Started the a/c and let the truck idle. Air was blowing cold for about 20 min. then began to warm. Drove home, about 3 miles, and it didn't cool off. When I got home, the compressor clutch was disengaged and the canister on the low side of the compressor was very hot. . Outside temp was around 90 degrees. Once everything cools off the system works.

 

[SunlitComet]

systems works as in the compressor starts to engage again till it fails?

 

[swampslider]

The whole a/c unit will work again until it gets hot, I'm thinking it gets hot. then the clutch disengages. This has only happened to me when sitting at an idle for a period of time or moving at or just above idle and when you shut it down and restart it before everything has cooled completely. If you start out moving 35 mph and above and only make short term stops, It seems to stay cold.

 

[swampslider]

Well I have a new discovery. Start out with Outside temp 83 deg with 75% humidity with clouds and 5 mph breeze. I spent two hours testing the electrical for the compressor and clutch. Every thing seemed ok. I started the a/c and within about a minute the low side tubing began the frost up all the way to the dryer.The temp on the pipe leading into the compressor was at 32 deg and falling pretty quick, about a degree every 40 to 60 seconds. I got a 10 degree reading from the duct. I realized the fan was on low. When I turned the fan on high it dissipated after 2-3 min. The second discovery was when I revved the engine to 2200 rpm the a/c clutch disengaged and wouldn't reengage until I reduced the rpm to around 1800. Does the 96 Yukon have a rev switch on the a/c? Could the heat that's developed cause the low pressure switch to stick until it cools enough to reengage? My next test I want to get some gauges hooked up to see what pressures are developing hi and low when this happens.