The AC on my 2001 F150 didn't work correctly so I bought a gauge and a bottle of AC juice and decided to charge the system. The AC starts out cold and turns warm. I put the gauge on the system and the needle goes to the red portion of the gauge. The AC will turn warm.

Is there a relay switch that quits functioning? Is there a code I could look at to determine the problem? Thanks

 

Go to the HVAC FAQs and read them.

Link is in signature below.

 

"red" as in too low of pressure, or too high of pressure ? You need two pressures, LO and HI side to diagnose a problem.

 

The gauge is what I bought for adding to the AC system. The gauge goes from OK to red which indicates too much AC has been put in system. The AC system is functioning fine and the gauge is registering every time the system calls for more cooling - then the system just goes to the red and the AC stops working.

 

You need to know the high side pressure also to get an exact analysis. Either you put way too much gas in the system, or you have a blockage (maybe in the expansion valve) that is restricting flow and causing the buildup of excess pressure.

 

The gauge is working normally. It is normal for the low side gauge to rise to the system's static pressure when the compressor stops running.

Go read the FAQs for an explanation.

 

True, this is why you need high side and low side gauges. It is beyond me why the walmart and autozone "adders" ever caught on and made money. Im sure they cause more trouble than they fix. "I'm an AC PRO", no they aren't. All joking aside man I was the tech, and low freon is usually not the cause of a/c issues. Like said, sounds like you have a blockage. Feel the lines on the highside to find it. Beware though, right out of the compressor esp. on a working system is HOT. The temperature changes is what makes the system work. Think of the compressor as only a pump, that is what it does the resultant pressure changes are where the magic happens. This is the cycle in small form. compressor to condensor (by the radiator) to orifice tube (this is where it should get cold) to in the cab to the evaporator to the accumulator (the big can by the firewall) to the compressor again then back over again. There is more to "know", but that is the general idea behind all refrigeration systems sense it's beginning.