95 SLS AC issues

[Devin O'Conor]

I had a new compressor installed on this car last summer. It was an AC Delco. It worked great last summer. This summer, it's not so great in town. It is semi cool but on the highway it is ice cold. Sounds somewhat normal but then I checked the pressures since it had been cold in town last summer. Here's what I found, 78° outside temp:

at idle 70 psi low side

105 psi high side

at 1500 rpm 45 psi low side

125 psi high side

Judging by the high side, it seems undercharged but why would the low side be so high? When the engine is revved, the low side goes down and high side goes up. But, it still cools very well at 30 mph and above. Someone mentioned it may be the reed valve. Is this common if the reed valves are the problem? Forgive my ignorance but if the problem is the reed valves, does it require compressor replacement? Anyone have any ideas? Kevin?

[Cadillac Jim]

If you had a new Delco compressor installed at a GM dealership, your compressor is probably had a lifetime warranty, parts and labor. If someone else put it on I don't know what the warranty is but the compressor itself is almost certainly still under warranty, if not the labor.

The reed valves are part of the compressor and, so far as I know, are not serviced except by overhauling the compressor -- which for a compressor in warranty means exchange. The factory shop manual compressor service has procedures for servicing the clutch and seals but not the reed valves, so I think replacing reed valves is a factory job.

There are other things that could cause the symptoms you describe. Does air flow freely through the condenser? How about the temperature sensor? Are you sure that the clutch isn't slipping? Have you checked for OBD II codes? Are you sure that the temperature control doors in the dashboard aren't sticking?

You can do a quick check by turning the temperature down to 60 F. That disables the temperature sensor and turns the cooling on full and the fan on high. If it blows cold air then, even at idle, it could be the temperature sensor or a connection. If there is no change, you still haven't eliminated the temperature control doors.

Here's how to pull the OBD II codes:

http://www.caddyinfo.com/readingcodes.html

[KHE]

The compressor is fine - you are undercharged. Add a can of R134a - be sure to burp the air from the charging hose prior to adding the refrigerant.

[Devin O'Conor]

Unfortunatly it was not installed by a GM mechanic. I'll habe to check on the warranty. It is OBD I but there are no codes. It isn't the doors on the dash because at idle the high side lines under the hood are not hot and low side lines are not cold.

Kevin, I wish it was a simple as an undercharge. I added a can of R-134a and very little change. At idle, high side is about 125 and low side about 70. When revved to 1500 rpm, the pressures still change as I said before and it gets cold. When dropped back to idle, the same old thing.

So, does this sound like a reed valve or something else?

I hate cars. I think I'll get a horse and buggy.

[KHE]

At this point, I would recover the refrigerant and weigh it to see how it compares with the specification. Check the orifice tube for debris while the system is discharged - that should provide a clue as to what's going on. If the pressures are fairly close to each other, the compressor may have failed.