Question for the automotive a/c gurus

farmer boy · Jul 26, 2016

Working on a Chevy Avalanche. A/C was barely working because it has a very slow leak. Added a can of refrigerant and the low side pressure was high, high side low. The high side and low side would nearly equal. Low side would come up to 107, high down to 112, before the compressor would click on. Figured the system was low, so I added a 6 oz can. Now the pressures are 45 on the low side, and about 250-270 on the high side. The A/C seems to work great, problem is that the compressor never shuts off. It just runs continuous, with the pressures staying the same.
I'm not sure If I'm low of high on charge. Maybe there's nothing wrong with this. Help me understand what is going on here. Thanks.

Allan in NE · Jul 26, 2016

Your readings are okay. When it's hot and humid, that compressor works harder.

Allan

jeffcat · Jul 26, 2016

If your system is really working well it will drop 50 degrees cooling from out side to cabin. My air gets so cold I have to turn it off now and then. Depending...You could have a parcaly pluged jet that meters the Freon. There are plenty of guys on here that have plenty of wrench time on these.

jimg.allentown · Jul 26, 2016

The condition you describe is about normal. On an average 75 degree day, the A/C will run about 40 on the low side and 225 to 250 on the high side. These pressures will increase on a warmer day due to expansion of the refrigerant.
Normally, the low side cycling switch is set to cut out when the pressure gets below about 22 to 25. It does not come back on until it gets back up to 40 or more.
When the compressor is off, the pressures will equalize as the high pressure liquid passes through the orifice into the evaporator.
Most R-134a systems will also have a high pressure cutout switch on the discharge hose. This is to keep the high side pressures from getting too high. On an overcharged system, high side pressures can quickly climb to 500 or so.
The best way to tell if the system is properly charged is when the return line coming from the evaporator back to the compressor should be cool and on a humid day will sweat. Then you know it is cooling.

Steve@Advance · Jul 26, 2016

Your presures depend on the ambient temperature. If you are reading them on a 90* day, engine revved up, air flowing through the condenser, they are right where you want them.

The compressor will start to cycle once the inside gets cooled down.

Super-H-Mike · Jul 26, 2016

Agree with the other comments, that sounds like normal pressures depending on ambient conditions.

RandyB(MI) · Jul 26, 2016

Don't know about your model but there were some Dodges that were designed to constantly cycle as long as ambient temp outside was 80 or above. Once below that would cycle normally. Probably to save on clutch wear and/or get by with smaller capacity system.

Question for the automotive a/c gurus

farmer boy

Well-known Member

Allan in NE

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jeffcat

Well-known Member

jimg.allentown

Well-known Member

Steve@Advance

Well-known Member

Super-H-Mike

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RandyB(MI)

Well-known Member

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