A/c question
Thread Starter
Instructor
Joined: Jan 2012
Posts: 108
Likes: 5
From: Lawrenceville NJ
A/c question
So, when I bought my car last month and had it checked out I was told the freon was a little low. The a/c seemed to work fine so I didn't do anything about. The a/c stopped blowing cold recently so I though I could charge it with some freon myself. I got one of the cans with a gauge and tried to add some to the system. I turned on the engine and connected the can. I noticed that the compressor would cycle on for about a second or two then turn off. I had the a/c on high of course. So I watched the gauge on the freon can and It would slowly go up into the zone where it should be, the compressor would cycle on and then the off and the pressure would drop to 15 psi and then slowly climb. And this would conitinue. I am not sure what this means? I thought that the pressure through the system would be constant and the compressor would stay on. I have a 1994 with the digital hvac controls. I did check the diagnostic mode and it showed no problems. Any suggestions?
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Cut off year was 93 for R12. 94 was the first year for R134a.
A/C system will ONLY have a constant pressure when it is off.
When on there is ever changing pressures, but you have a low side and a high side. A fast cycling compressor is one symptom of low refrigerant.
Low side pressure will slowly climb between compressor cycles. In a typical system if the pressure falls below 20psi in the system it will shut the compressor off, to protect it from low refrigerant and to prevent evaporator freeze up. It will turn back on once pressures reach about 40 or so. The low side pressures should vary between about 20-50 psi. With around 30 being the average maybe a bit more. Depends on the system.
If your A/C is low you have a leak. Inject dye and use a black light wearing yellow glasses to find it. I do NOT recommend A/C system sealers. They can cause more trouble than they fix, ever see a orifice tube plugged up with that crap, I have.
A/C system will ONLY have a constant pressure when it is off.
When on there is ever changing pressures, but you have a low side and a high side. A fast cycling compressor is one symptom of low refrigerant.
Low side pressure will slowly climb between compressor cycles. In a typical system if the pressure falls below 20psi in the system it will shut the compressor off, to protect it from low refrigerant and to prevent evaporator freeze up. It will turn back on once pressures reach about 40 or so. The low side pressures should vary between about 20-50 psi. With around 30 being the average maybe a bit more. Depends on the system.
If your A/C is low you have a leak. Inject dye and use a black light wearing yellow glasses to find it. I do NOT recommend A/C system sealers. They can cause more trouble than they fix, ever see a orifice tube plugged up with that crap, I have.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
A/C shops have an electronic sniffer that can detect refrigerant leaks, or you can buy one of these:
http://www.harborfreight.com/electro...tor-92514.html
http://www.harborfreight.com/electro...tor-92514.html
Thread Starter
Instructor
Joined: Jan 2012
Posts: 108
Likes: 5
From: Lawrenceville NJ
Thanks for the replies. I wonder if the fact that it was only 60 degrees out when I was trying to charge the system had something to do with it. I will see what happens when it gets warmer out. I was hoping I could get away with just charging the system then having to pay a large repair bill since I don't have the equipment to fix it.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Damn - an Electronic Detector for 70 Bucks! I've just taken advantage of the Shops around here that will do it for free. Anyway, you really need a manifold gage set to know what the charge is and 70 degrees is a much better ambient for charging (80 is better). If it is low, keep it from cycling by jumpering the Low Pressure Switch. You also want the radiator fan(s) cranking, a minimum of 1200 rpms (steady) and the system on MAX. Service Manuals outline expected performance for outside air temp. A high side of 2.25 to 2.5 times ambient at the Condensor is a rough measure of a full system; ie, if it's 80 at the Condensor. 180 to 200 psi on the high is what you should aim for. You should also pick up a digital thermometer (5 Bucks at your Grocery Store) and stick it in the Center Vent. Finally, for a system that suddenly stops making cold air, verify the temp door is still moving. Remove the Blower Module or Resistor Pod from the Evaporator Case and look inside to see/verify that the door moves between the warmest and coldest settings.
