A/C short cycle

[wstefanko]

Hi all, I have a 99 Tahoe with rear a/c. A couple of weeks ago my back a/c was blowing cold and the front was warm. I called up GM to bend their ear. They said sounded like low on freon. They were right and at no charge. Bought a refill kit with a gauge. I was low on freon. Refilled to spec and both front and back were blowing cold. The other day I went out and both front and back were blowing warm and my compressor was short cycling(5 seconds on and 5 seconds off) I jumpered the cycling switch(not sure of the exact name) and the compressor would constantly but my system would not get cold. I do not see any leaks and I have around 45psi so I know I am not low on freon. Any thoughts on where to go to next? Thanks.

 

[lesterl]

what psi with compressor off? if you had to call gm to get the info it was low, perhaps you should find someone in a shop who could look at it for ya. That being said, I would get some dye and recharge if it is low to look for leak.

 

[wstefanko]

When the compressor is not running it shows 60-70 psi, when it kicks on it pulls it down to 25-30 psi then builds back up to around 45psi then it will cycle off. I know my way around the mechanical part of cars but HVAC is new to me. I just do not see why it shows normal psi on the gauge and won't blow cold. My thought is a blockage somewhere in the lines which I will then let a technician handle it so they can evacuate the system. I just hate throwing money away right if there is a simple fix someone else has encountered. I do not want to just swap parts like a lot of people/companies.

 

[lesterl]

Yeah, I know my way around a few things also, learn alot as I go on a lot of things, the 70ish PSI around comp off and 30 or so running sounds right, when do you get the 45psi reading? Compressor running? Perhaps you have it overcharged. If the orifice tube or expansion valve were plugged/ sticking I would think the low side would drop as there would be a loss of return pressure.

 

[wstefanko]

Because it cycles on and off every 5 seconds it was hard to get the 45psi reading. It was consistent when I jumpered the switch so the compressor would run constantly I get 45psi. Do you think I should put the leak stuff in and check for leaks first? Then if I see no leaks take it in an have it checked? I imagine I would over pay to get it leak tested at a shop.

I have a hard time trusting mechanics. My brother in law's good friend has a shop. When I had him replace a wheel hub and axle seal(because it failed inspection and I did not have enough time to do it) he did the work and within 6 months the seal was leaking again, he tried everything in the books to not have to take my truck apart again to fix his mistake. I got tired of arguing and did it myself. If a friend could do that how could I find a trustworthy stranger.

Sorry about my rant.
Thanks again.

 

[lesterl]

I would say you need a real set of gauges to see what the high side is doing as well....