Bizarre ac behavior

[drdoom1337]

Hello all,

I have lurked for many years, but finally broke down and made an account because I'm stumped.

I have a 2000 k2500hd. My ac system gave up the ghost last year, there was a leak somewhere and then fall / winter came so it wasn't important.

I had a shop recently run a test for me and as expected, the compressor was leaking at its halfway point. I replaced the compressor 3 days ago and noticed that the service valve had a leak on the low side. I jiggled the schraeder valve and that stopped. Continued filling the system. Coldest ac I've ever felt in my life, until today

Noticed that the system was getting warm today. On my way out of work, I hooked the simple freon refill device up to the low side and there was 0 pressure. Everything leaked out. I drove home with the ac off, recirculation unclicked, but my compressor clutch was still running and i kept hearing a hissing noise from under the dash where the evaporator is.

Why would I be getting a leak / hiss noise and why would the compressor keep running if there's no pressure or refrigerant in the system? Is the evaporator blown?

 

[someotherguy]

You're 100%, and I mean 100% sure the compressor was still running? That would mean your low pressure switch is possibly shorted which isn't exactly a common situation, or could be the A/C control panel is bad - but I'd hope (haven't looked over the diagrams) the low pressure switch would be wired in a way that would negate any erroneous input from a bad control. Also possible the air gap on the new compressor's clutch is too tight so it's engaging when it shouldn't.

So with the A/C off you can pop your hood now with the engine running and witness the compressor clutch spinning? If so (shut the engine off first) try disconnecting the electrical connector to the clutch and start the truck back up, see if it's still spinning. It should stop. If not, it's mechanically engaged due to the air gap being too tight. I'd resolve that immediately as it continuing to run without adequate refrigerant charge is gonna roast it quickly as it won't get lubricated.

The leak in the service port is kind of common on old hoses. That should've been your cue to replace it.

Richard

 

[Ranger550]

Most likely you have a bad low-pressure switch. Your compressor should NOT be running with zero pressure. The L-P switch should have shut your magnetic clutch down. You need to make sure that your A/C compressor is not operating until the issue is solved. I'd buy or borrow an AC gauge set and see what it says. I hope it's not the evaporator as they are a real b***h to replace. I'd replace your Schraeder valves, if that may be where the leak came from. My lowside leaked last year but my K-1500 is 25 years old.

 

[Schurkey]

The above info is good.

I would add that I'm suspicious of your "0 pressure" reading. First Guess: You didn't get the gauge properly connected to the service valve. The system HAS some pressure, perhaps not enough to properly cool, but enough to allow the compressor to run.

 

[drdoom1337]

I actually do own proper gauges, and i can perform the reading agwin. I just did not have them to hand at that time.

I still don't believe the clutch gap or a bad sensor (I've replaced the low pressure sensor) would cause the area under the dash to hiss even with thr AC off. Could the evaporator be looking for freon because the compressor keeps running ?

I could try shooting dye through the system with a half can, but if there's an internal leak under the dash there's no obvious way to see it ?

 

[someotherguy]

If your compressor is running when it shouldn't be on a low charge, I wouldn't be surprised there are unexpected noises from the system. Let's deal with facts and discover whether the compressor is actually running when it shouldn't be, and take this in logical steps instead of wondering what's going on.

Richard

 

[Ranger550]

I actually do own proper gauges, and i can perform the reading agwin. I just did not have them to hand at that time.

I still don't believe the clutch gap or a bad sensor (I've replaced the low pressure sensor) would cause the area under the dash to hiss even with thr AC off. Could the evaporator be looking for freon because the compressor keeps running ?

I could try shooting dye through the system with a half can, but if there's an internal leak under the dash there's no obvious way to see it ?

Maybe enough of it would come out of the climate control box drain hose at the bottom of the firewall and drip on the ground?

 

[Ranger550]

The above info is good.

I would add that I'm suspicious of your "0 pressure" reading. First Guess: You didn't get the gauge properly connected to the service valve. The system HAS some pressure, perhaps not enough to properly cool, but enough to allow the compressor to run.

I wonder at what pressure the low-pressure sensor shuts the mag-clutch down?

 

[Schurkey]

Depends on whether the low-pressure switch is intended for R12 or R134a. R12 would be higher pressure than 134, 40-ish psi vs. 22 psi, I think.

 

[Schurkey]

Maybe enough of it would come out of the climate control box drain hose at the bottom of the firewall and drip on the ground?

Get an electronic leak detector, poke the probe into the drain hose nipple. Don't need dye, just some amount of refrigerant charge.