A/C gremlin

[runningred92]

Ok so my system has been retrofitted to accept R-143-a by the previous owner and about this time every year I need to recharge the system. I bought a can of R-134-a and went to recharge it. With my truck running and a/c on high I hooked up the hose with an in-line pressure gauge to the L port and instead of being low it was at 100psi. UHOH! I left the air running on my way home and noticed that when I am moving the air blows at least 20 degrees cooler but as soon as I stop it goes back to blowing HOT. My dummy temp gauge on the dash is normally below the N and with the air running it moves almost to the N. Now I know the engine is at a good operating temp I have had it checked so as long as it stays right there I know its ok. Is my compressor not running correctly or??? I know a little about a/c systems but could use some help with this one. Could it be as simple as just removing coolant to proper operating pressure? Appreciate some help with this one.

-Andrew

 

[Tshark299]

If you don't find an answer here, try posting in the A/C & Heater Systems forum. I've had good luck getting AC-specific problems solved there.

 

[arco777]

Ok so my system has been retrofitted to accept R-143-a by the previous owner and about this time every year I need to recharge the system. I bought a can of R-134-a and went to recharge it. With my truck running and a/c on high I hooked up the hose with an in-line pressure gauge to the L port and instead of being low it was at 100psi. UHOH! I left the air running on my way home and noticed that when I am moving the air blows at least 20 degrees cooler but as soon as I stop it goes back to blowing HOT. My dummy temp gauge on the dash is normally below the N and with the air running it moves almost to the N. Now I know the engine is at a good operating temp I have had it checked so as long as it stays right there I know its ok. Is my compressor not running correctly or??? I know a little about a/c systems but could use some help with this one. Could it be as simple as just removing coolant to proper operating pressure? Appreciate some help with this one.

-Andrew

With the truck idling and AC on full blast, does the compressor stay running steadily? If so it's probably fine.

If it cycles on and off, the pressure/refrigerant is low (or possibly high in this case). I find that the sensors built into the system know better than some cheap AC gauge what's best.

 

[runningred92]

Arco-Yes the compressor stays running constantly. Are there any vacuum lines involved in the cooling sequence somewhere and its possible I have some criss -crossed at the vacuum tree? I replaced some a while back when I noticed some were just old and leaking but thought I put them all back where they but doesn't mean I did.

 

[arco777]

Arco-Yes the compressor stays running constantly. Are there any vacuum lines involved in the cooling sequence somewhere and its possible I have some criss -crossed at the vacuum tree? I replaced some a while back when I noticed some were just old and leaking but thought I put them all back where they but doesn't mean I did.

I don't know of any vacuum lines involved with the A/C (except for the actual ducting and the 1994's heater core bypass valve).

I would check your charge level with another gauge if you have one. If it still shows high, maybe there's a blockage in the line? Usually the only debris in the system comes from the compressor breaking down internally and the orifice tube will get clogged up. I can't think of any way to check that tube without depressurizing the system but, like the main issue, I'm sure someone smarter than me will chime in here on what might be wrong.

 

[runningred92]

Yeah I will check it with another gauge tomorrow.The compressor very well could be breaking down it is the original I think. Like I said the guy before me just did the cheap retro fit conversion on the a/c so it probably wouldn't hurt to swap some stuff out anyways. But maybe its just my gauge and another one will tell me its just low. But if it was just low wouldn't the compressor be cycling on and off a lot. Thanks for your help.

 

[runningred92]

So I am still needing some help. I finally got some time today to keep troubleshooting the A/C. I know my gauges are good now so I hooked it back up just to make sure it read the same and it did. The other day when I first noticed the low pressures were really high as I started driving while the A/C was still on full blast the air started blowing cold again. So today while I had the gauge hooked up I pressed the gas and brought it to 2500 to 3000 rpm. The gauge instantly dropped to about 40psi from 100psi and started blowing cold. So with that being said I was hoping that would help point to a specific problem or at least give more of an idea of where I need to check next.

 

[safn1949]

The only thing I can think of is a faulty orifice tube as that is what separates the high and low side.

 

[runningred92]

I talked to a guy that claims to be a mechanic and he said since the pressure drops when I give it gas (does not need to be moving) the pressure drops and the air turns cold that the compressor clutch could be slipping. Could that be it? Is it possible to swap just the clutch or do I need a new compressor if that is the case. Since my compressor still seems to work when the rpm is up I would hate to replace the whole thing if I don't have to. Thanks for your help.

 

[safn1949]

I would think that the clutch would slip when you rev it up as the pressure will also rise.Check the clutch gap,I don't know what the spec is but it is easy to check with a set of feeler gauges.