equal pressure both sides of the gauges

[craftsman]

I'm just starting to diagnose a 2006 Hyundai Elantra, but could use a little help. The clutch engages and spins the compressor. The gauges were showing equal on both the high and low sides. They were at 35 each, then I added a little r134a and they both said 40. So, am I looking at a failed compressor, or could the expansion valve just be stuck open?

Appreciate any advice.

[james89dx]

You're not opening the valves on the manifold gauge set are you?

[craftsman]

At one point when i thought maybe I'd add a little r134a, I did open the low side gauge to allow the r134a in. But the rest of the time they were both closed. When I added more in the low side, both side immediately went up together and I was suprised. If I didn't see the pump engage, I'd think it was dead since it seems to have little effect on the pressures. I'm going to try take a look at the expansion valve and see if there is a chance its stuck open.

[Tim]

Make sure you're getting proper connections wiht your gauges. Low 35 and high 35 seems odd for a piston compressor.

[JohnHere]

I don't think the compressor would run with only 35 to 40 PSI on the high side. Looks like you're not getting true pressure readings, due either to a malfunctioning manifold gauge set or to faulty connection(s), as Tim suggested. Double-check your hoses to ensure that they're facing the right direction and depressing the Schrader valves enough to let system pressure reach the gauges. If that checks out, borrow another manifold gauge set from a friend or from AutoZone and take another reading.

[craftsman]

I did some more testing tonight, and what I found was that basically the compressor does nothing to the pressure readings. I was getting 35 psi on both sides the compressor not running. I added r134a with the pump off and got both sides up to 45psi. Then I turned turned on the AC and heard the clutch engage and saw the pump spin, but it did nothing to the pressure. Could the pump fail in a way where it would just not pump anything without being seized up?

[craftsman]

Not unlikely at all. Modern comps do away with piston rings and have a polymer coating either on the piston or on the cylinder as a means of sealing. If this one wears down too much you get a compressor that is only good at making noise and nothing else. I think prolonged running in this condition could also possibly result in a seizure since the oil flows along with the refrigerant across the system and no pumping action means no flow, more so if you have the fixed displacement crankcase-free compressor.

Thanks, that confirms what I was thinking.