A friend wanted me to look at the A/C on her 2001 E320, and when I hook up the low pressure hose with the engine off the gauge pegs!
With the engine on the compressor never turns on.
Looks like there is plenty of Freon.


At first I suspected the expansion valve, but in retrospect I think that would only affect the high side. Don't see how it could be the compressor because it isn't even coming on (unless there is a check valve in the compressor somewhere.


Jim Lane, Frosty, any ideas anyone?

 

High side readings?

 

Normal range, like 150.

 

Electrical fault somewhere. There's AC switch, temp control, high pressure limit, low pressure limit, electric clutch.

You need the wiring diagram and a meter or test light and trace it out.

On pressure, the pressure in the system at rest depends on the temperature of the coolest part. There should be some liquid in the system, so the pressure would be the vapor pressure of the refrigerant at that temperature.

Running, low side is near the vapor pressure at the temp of the evaporator, and high side at the temp of the condenser.

 

New csr, you need pull diagnostic codes.
Look at the compressor front. W engine on, accurate max. Does the clutch engage?
M

 

Somebody charged the system with air in it.

 

What is the high side reading? At rest both sides should be the same if it also reads 150psi it's over charged.

 

It's not as simple as that. 150 psi is the vapor pressure of R134A at about 112° F. It's not unreasonable for the cab temp and the compressor temp to be that or higher this time of the year, especially if the engine has been running.

First things first, as Sam said, look at the compressor and be sure it's turning. the hub as well as the belted pulley. If it is, probably the compressor is bad, or something is totally plugged up.

If the hub is not turning, then check for 12V at the clutch connector.
If there, the clutch is bad.
If not, then troubleshoot the electrics and find out why.

Pressures don't mean a thing unless temperature and motion is also known. (Except 0 psi standing still and warm, that means there's a hole in it somewhere_)