2002 AC Question

[teafreak35]

I have a 2002 Astro. About a week ago, the air stopped working. Checked under hood and compressor clutch was not engaging on compressor at all. Checked what I assume to be low pressure port (on accumulator). Gauge showed that refrigerant was low so I added a can of refrigerant. Compressor began running in short spurts, but still wasn't cooling and gauge still showed pressure to be low so I added another can. At this point, pressure was at 35 psi at about 85 degrees Fahrenheit and compressor was coming on and running for a few seconds at a time, but there was only a small difference in the air that was blowing. I didn't have another can of refrigerant so I left it as it was.

This morning I went out to check the system again...again, the compressor is coming on and running in very short spurts (like one second) and then cycling off. The pressure on the port is what has me confused. When the compressor Is NOT running, the pressure runs up to about 55 psi...when the compressor comes on, the pressure drops to about 10 psi. Temp outside is about 70 degrees. What's going on here?

This van is equipped with rear air as well in case that matters, but only the one compressor.

[old_master]

The clutch cycling system on your vehicle is extremely sensitive to the amount of refrigerant charge. Too much is just as bad, if not worse, than too little. The ONLY way to know how much refrigerant is in the system is to drain, evacuate, and charge it with the proper amount of refrigerant and PAG150 oil.

If the system is low on charge, it has a leak. While there is still refrigerant in the system, now would be the time to install fluorescent dye, then use a black light to locate the leak. The Harrison HT6 compressor used on your vehicle is known to leak where the two case halves come together, commonly called a "belly leak", eventually they all do it.

The switch on the accumulator is the clutch cycling switch. Before the system is turned on, pressure in the system, (both high and low side), will be very close to the ambient temperature, ie: 85 degrees outside equals 85psi in the system. When the system is turned on and the clutch engages, high side pressure increases and low side pressure decreases. The cycling switch is designed to turn the compressor clutch off when low side pressure drops to 22psi. After the clutch shuts off, low side pressure increases and high side pressure decreases. When low side pressure rises to 42psi, the cycling switch turns the compressor clutch on. By design, the system must have a minimum of 42psi for the clutch to engage. With this type of system, it must have the correct charge to diagnose problems.

Depending on ambient temperature, engine coolant temperature, relative humidity, and everything is in good condition, and operating correctly, and 1,500 engine rpm low side pressure should cycle between 22psi and 42 psi. High side pressure will vary depending on atmospheric and vehicle conditions, and should not exceed approximately 250psi just as the clutch disengages.