A/C clutch will not cycle off

[skychair]

I cannot figure out why my A/C clutch will not cycle. (99 Yukon, E-fans installed)
I had a R134a leak thru a defective 'O' ring and the system evacuated its self over nite.
No pressure at the low or hi manifold connections .
Replaced the 'O' ring, and the recycle switch on the Accumulator, vacuumed it down to 29" it held over nite.
Re charged with 64 Oz of R134a.
Low pressure @ ambient temp of 81 degree's is 35, hi pressure is 133.

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If I slide the connection on and off the the switch the clutch cycles on/off as do the fans,
a jumper wire does the same thing, so the clutch functions properly.
Drove it on a 20 mile round trip to test, it took 9 minutes for the system to get 'cold', it's never cold immediately.
Temp at center vent 38-42 degrees.

There is a switch on the back of the compressor, that I have never had a problem with, could this be the culprit?
It's like the Hi pressure cant get Hi enough to kick off the compressor??? This switch bad???
Any thoughts........
I know a low-low and a low-hi indicate a low charge, but I put in 5-12 oz cans and 4 oz (weighed) from the last can.

THE BIG question will I sustain damage if the A/C runs continuously???? Like Interstate travel?
I really don't want to damage the compressor.
If you have a suggestion.........
Ron

 

[rags77]

Since engine temp is cooler with the electric fans running ...some A/c systems I believe has an temp sensor that when at warm temp causes the ac compressor to shut off..

 

[L31MaxExpress]

Using R134a in a dual evaporator system the compressor is unlikely to cycle in weather hotter than 80°F and if it does it will not cycle often. Was not until I switched to R152a that I saw a dramatic cooling increase and frequent a/c cycling at higjway speeds. The low side pressure just does not drop enough to cause the compressor to cycle. Cut-out is at 24 psi IIRC. I put an older adjustable switch on my Express van to keep the front evaporator from freezing running R152a. I had to raise the cutout pressure from 24 psi to 30 psi. With the stock cutout pressure my accumulator was frosting in 90°F weather at idle with the blower on high on both units. With the duramax fan blade my pressures were about 130/25 on a charged by feel system. Accumulator same temp as evaporator inlet.

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[df2x4]

Using R134a in a dual evaporator system the compressor is unlikely to cycle in weather hotter than 80°F and if it does it will not cycle often. Was not until I switched to R152a that I saw a dramatic cooling increase and frequent a/c cycling at higjway speeds. The low side pressure just does not drop enough to cause the compressor to cycle. Cut-out is at 24 psi IIRC. I put an older adjustable switch on my Express van to keep the front evaporator from freezing running R152a. I had to raise the cutout pressure from 24 psi to 30 psi. With the stock cutout pressure my accumulator was frosting in 90°F weather at idle with the blower on high on both units. With the duramax fan blade my pressures were about 130/25 on a charged by feel system. Accumulator same temp as evaporator inlet.

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Are there any modifications necessary to run the dual evaporator GMT400 systems with R152a instead of R134a? Any issues to consider for those of us who have switched to soft lines to and from the rear evaporator?

For what it's worth, the compressor in my Suburban never cycles when it's over 80 degrees outside either. Its performance is pretty bad the last few years even though the refrigerant levels are fine. My mechanic believes it's the compressor getting weak or leaking internally. I'm going to replace it at some point, but if I could improve performance by switching refrigerant types that would be neat.

 

[L31MaxExpress]

Are there any modifications necessary to run the dual evaporator GMT400 systems with R152a instead of R134a? Any issues to consider for those of us who have switched to soft lines to and from the rear evaporator?

For what it's worth, the compressor in my Suburban never cycles when it's over 80 degrees outside either. Its performance is pretty bad the last few years even though the refrigerant levels are fine. My mechanic believes it's the compressor getting weak or leaking internally. I'm going to replace it at some point, but if I could improve performance by switching refrigerant types that would be neat.

My Express conversion van has a GMT400 based A/C system with an aftermarket rear system that uses R134a barrier style hoses for most of its length. The R152a is duster air. Disclaimer it is mildly flamable. But so is R134a mixed with highly atomized Pag oil. The R152a requirement is roughly 65% of R134a in the same system. The only change I made to the system was a sticky label to identify it as R152a where the R134a label sits and the swap to the adjustable cycling awitch. That being said I had an aftermarket Valeo compressor on mine that has been on it since 2006. It still works extremely well although the swash plate has been knocking for about 4 years now. The R152a runs at a lower pressure and actually cut the volume od the knocking sound in half. I have actually played around with the orifice tube size as well on the front evaporator. I spend alot of time at idle or near idle. The white 0.072" GM orifice is the worst for idle cooling. The ford Red 0.057" is best for idle cooling althougj the system cycles too frequently on the highway with it. The Blue ford 0.067" works well on the highway and dropped the vent temps about 4-5°F ay idle. With the 25% underdrive crank pulley I have the Ford Orange 0.062" orifice gave the best all around performamce on R134a and R152a. With each orifice I charged the system until the evaporator inlet and outlet were approximately the same temperature with the blower on high, recirculate and the accumulator should also be cold to the touch with proper system charge. When the system gets enough refrigerant in it you can actually watch the high side pressure drop as the cool vapor starts reaching the compressor

 

[df2x4]

My Express conversion van has a GMT400 based A/C system with an aftermarket rear system that uses R134a barrier style hoses for most of its length. The R152a is duster air. Disclaimer it is mildly flamable. But so is R134a mixed with highly atomized Pag oil. The R152a requirement is roughly 65% of R134a in the same system. The only change I made to the system was a sticky label to identify it as R152a where the R134a label sits and the swap to the adjustable cycling awitch. That being said I had an aftermarket Valeo compressor on mine that has been on it since 2006. It still works extremely well although the swash plate has been knocking for about 4 years now. The R152a runs at a lower pressure and actually cut the volume od the knocking sound in half. I have actually played around with the orifice tube size as well on the front evaporator. I spend alot of time at idle or near idle. The white 0.072" GM orifice is the worst for idle cooling. The ford Red 0.057" is best for idle cooling althougj the system cycles too frequently on the highway with it. The Blue ford 0.067" works well on the highway and dropped the vent temps about 4-5°F ay idle. With the 25% underdrive crank pulley I have the Ford Orange 0.062" orifice gave the best all around performamce on R134a and R152a. With each orifice I charged the system until the evaporator inlet and outlet were approximately the same temperature with the blower on high, recirculate and the accumulator should also be cold to the touch with proper system charge. When the system gets enough refrigerant in it you can actually watch the high side pressure drop as the cool vapor starts reaching the compressor

Thanks for the info!

The compressors in both of my '97s have a knocking sound when they're running as well. My red truck has done it since I've owned it, while the Suburban just started in the past couple years. The red truck cools great while the Suburban struggles. I think a lot of that has to do with the dramatic difference in cabin air space, though. Plus the addition of the rear evaporator.