AC problem

[wtnhunt]

On our 98 chevy truck the compressor runs when it is turned on, but does not stay running, kicks on and off and it is blowing warm air. Figured it was just low on refrigerant so I was going to try and recharge it yesterday, but the gauge showed around 47-50 lbs when the compressor was kicking off putting it in the warning range so I did not attempt to put any of the R134a in it. When the compressor kicked on it would drop down to around 0-2 lbs, having me thinking maybe it just needs refrigerant and that might have the compressor actually stay engaged if it was charged, but wondering if the system need evacuated before attempting to charge it with the pressure in the warning range when the compressor kicks off. Also noticed the ac lines normally cool to touch were pretty warm.

[redkneck]

Just shooting from the hip here, I'm not a car A/C guru, but I have had to jump the compressor clutch with 12V from the battery. Normally I would think your low pressure switch would let it run with that kind of pressure when it's not engaged, but sometimes they get out of whack. Maybe try to jump the clutch out to keep it engaged and try to get a good charge. Your not going to damage it, the only real damage would come from having little to no refrigerant in the system and therefore no oil circulating back to the compressor. You'll probably be in the 35 psi range on the low side if it's not to hot outside. Hopefully it's not too bad. New compressor warranties are generally only given when you change the compressor, receiver dryer, clean expansion valves, flush, and all that crap plus provide documentation it was done by a certified shop, etc. A real pain in the butt and will set you back around 750 I'd guess for your truck.

[wtnhunt]

Just shooting from the hip here, I'm not a car A/C guru, but I have had to jump the compressor clutch with 12V from the battery. Normally I would think your low pressure switch would let it run with that kind of pressure when it's not engaged, but sometimes they get out of whack. Maybe try to jump the clutch out to keep it engaged and try to get a good charge. Your not going to damage it, the only real damage would come from having little to no refrigerant in the system and therefore no oil circulating back to the compressor. You'll probably be in the 35 psi range on the low side if it's not to hot outside. Hopefully it's not too bad. New compressor warranties are generally only given when you change the compressor, receiver dryer, clean expansion valves, flush, and all that crap plus provide documentation it was done by a certified shop, etc. A real pain in the butt and will set you back around 750 I'd guess for your truck.

So what your saying is to run a jumper from the ac compressor to the battery to keep the clutch engaged and charge it while it is jumpered? Guess I am kind of concerened/nervous about adding more refrigerant and pressure since when the compressor is kicked off it goes to pressures that are in the warning range on my gauges, or is that normal? Don't guess I can remember encountering this kind of thing before when adding refrigerant to a vehicle. With the gauge showing around 2 lbs(on the low pressure side) when the compressor is kicked in, I kind of figured the reason it is kicking off is because it is low.

[redkneck]

Remember 2 things.

You are on the suction side of the system. The compressor must be running to charge it. When the compressor kicks in, the suction pressure should drop.

The pressure you read with the engine off has zero to do with how much refrigerant is in it. Look at the temp/pressure chart below and you'll see what the pressure should read at a given ambien temp. In other words if you take a drum of 134A freon and set it out in 81.97 degree temp, you'll read 90PSI. If you take out most of the liquid, it will still evaporate to the same 90PSI. So if you are reading 50 psi at the 80 degree mark, this should say you are really low on refrigerant to the point there is no liquid left to evaporate and build pressure.

http://www.glacierbay.com/ptchart134a.asp

I hope that wasn't too rambling. I tinker with my own a/c stuff but really dont work on vehicle systems much other than occasionally charging my own stuff. The reason you're trying to get to the 35 range or so on the suction side is that the refrigerant should be in the neighborhood of 40 degrees as you can see on the chart.

[redkneck]

One more thing. I've only jumped out one compressor that I had a low pressure cut-out switch that was not working right. Not sure I totally understood the original post, but your compressor should not turn off if you have the valve open to the can which should supply enough pressure to satisfy the switch.

[wtnhunt]

Remember 2 things.

You are on the suction side of the system. The compressor must be running to charge it. When the compressor kicks in, the suction pressure should drop.

The pressure you read with the engine off has zero to do with how much refrigerant is in it. Look at the temp/pressure chart below and you'll see what the pressure should read at a given ambien temp. In other words if you take a drum of 134A freon and set it out in 81.97 degree temp, you'll read 90PSI. If you take out most of the liquid, it will still evaporate to the same 90PSI. So if you are reading 50 psi at the 80 degree mark, this should say you are really low on refrigerant to the point there is no liquid left to evaporate and build pressure.

http://www.glacierbay.com/ptchart134a.asp

I hope that wasn't too rambling. I tinker with my own a/c stuff but really dont work on vehicle systems much other than occasionally charging my own stuff. The reason you're trying to get to the 35 range or so on the suction side is that the refrigerant should be in the neighborhood of 40 degrees as you can see on the chart.

That is reinforced by the warm to touch lines and no condensate on those lines. Never tried opening the valve from my charging can. Will have to get back into it this weekend and see if I try to open the valve if it will hold the compressor clutch in.

[redkneck]

I'll bet you that will work. The refrigerant carries oil through the system to keep the compressor lubed. The real danger is running out of refrigerant/oil and burning up the compressor, that's the reason for the low pressure cut-out switch. Most of the time when you're real low you'll have to dump freon into the system to get the switch on, cuz as soon as the compressor pumps, the suction side of the system is going to drop big time in pressure. Don't be afraid to turn the bottle upside down just a little to drop some liquid in there. Just turn it right side up again and watch your pressure till you get it right.

[Ravin R10 man]

freon is low

[wtnhunt]

Charged her up this morning and ice cold ac once again. Pressure never went over 46 psi this morning clutch/compressor off, got it to 25 psi(full) with the clutch kicked in.

[Ravin R10 man]

:cool2:

[redkneck]

Nice when you got cold air this time of year. Just don't ever let it run completely out, then you'll get moisture and air in the system and really have to do some work next time around.