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Question About New Compressor Install & Readings

ozz316 on Tue June 21, 2011 10:16 PM User is offline

Year: 2001
Make: International
Model: 9600
Refrigerant Type: R134
Ambient Temp: 83
Country of Origin: United States

I am working on the a/c on a truck for work. We had a compressor failure so I replaced the compressor (sanden), clutch, expansion valve, accumulator, flushed condenser and had checked for blockages as well as the evap coil and all lines. Evacuated the system obviously and recharged with lbs 8 oz per manufacturers recommendation as well as replaced oil for lines and condenser and evap coil. Compressor had oil in it from dealer. After all this compressor starts winning after a short amount of time. Checked pressures and am getting approx. 45 psi when clutch is engaged. Clutch disengages and pressures go to 90 psi then clutch kicks back in. High side pressures never get over 115psi. and fan never turns on. Could I possibly have a bad compressor on my hands?


bromodragonfly on Tue June 21, 2011 10:58 PM User is offlineView users profile

Does any cooling occur during all of this?

It sounds like a bad compressor. A whining sound is never good. Is there a certain pressure on the high/low side that is causing the compressor to cycle? Is the discharge line of the compressor really hot?

If your compressor is variable displacement and has a control valve, someone here will have a method of testing the control valve itself. It is supposed to sense the system pressures and adjust the compressor flow rate accordingly. I would assume that if it was somehow stuck on a low flow setting, you would have a low discharge pressure.

I also found this from a Sanden Compressor Service PDF on Google. Applies to the following models: SD7B10, SD7H13, SD7H15/HD, SHD SD7B10, SD5H09, SD5H11, SD5H14

"Compressor suction or discharge valve breakage will cause a clacking sound at idle.
If head gasket failure occurs, discharge pressure will be low and suction pressure will be high
at idle.
Valve and gasket condition can be checked as follows:
Connect gauge set to suction and discharge service valves.
Run compressor for 5 minutes at idle and stop.
Observe time for discharge pressure and suction pressure to equalize.
If less than 2 minutes, in a TVX system, a valve or gasket may be damaged. CCOT systems will equalize more quickly."

There is no knowledge that is not power

ozz316 on Tue June 21, 2011 11:15 PM User is offline

The clutch also locks up periodically when the compressor starts whinning, sounds like a bearing going out in a pulley. The compressor kicks on around 90 psi and drops to about 40-50 psi runs there for a while and then kicks off and pressures go up to 90 rinse and repeat. The High side pressure doesn't really move much from 100 psi. My notes are at work so I am going by memory.

I did the no no hand test to the line going from the compressor to the condensor and it was pretty hot, the line leaving the condensor was a little cooler but not alot. I didn't get my digital thermometer out to check actual drop. The temperature was cooler down the line to the expansion valve, but never cool.

mk378 on Tue June 21, 2011 11:17 PM User is offline

If it were just a bad compressor, it would sit there and spin and not make much pressure, but it would not cycle on and off. Something is turning it off, possibly the high pressure switch. You need to look at the layout of the system, there could be a blockage so the compressor experiences abnormally high pressure but your gauge does not.

ozz316 on Tue June 21, 2011 11:26 PM User is offline

We went ahead and replaced both the high and low pressure switches as well as the fan switch. Everything has been flushed and checked or is new. Could bad oil that came in the compressor or not enough oil in the system cause any of these issues?

mk378 on Tue June 21, 2011 11:30 PM User is offline

There is noise from the compressor, clutch slipping, and cycling off-- all of that suggests the compressor is working against a very high pressure which you don't see at the service port because the condenser is blocked.

ozz316 on Tue June 21, 2011 11:37 PM User is offline

Should I connect my high side gauge to the fitting at the compressor instead of at the accumulator to see if I get a different reading?

Edited: Tue June 21, 2011 at 11:45 PM by ozz316

bromodragonfly on Wed June 22, 2011 12:06 AM User is offlineView users profile

To the fitting on the compressor

There is no knowledge that is not power

ozz316 on Wed June 22, 2011 12:07 AM User is offline

Sorry meant to say service port. There are two high side service ports, one at the compressor and one on the accumulator dryer.

bromodragonfly on Wed June 22, 2011 12:12 AM User is offlineView users profile

If your high pressure cutout is located closer to the compressor, and you're taking your readings at the receiver, then MK378 is totally correct.

Now I'm curious how well did you flush?

Not enough oil/bad oil would cause a problem over time, but it shouldn't prevent the compressor from reaching a nominal discharge pressure right now.

There is no knowledge that is not power

Edited: Wed June 22, 2011 at 12:15 AM by bromodragonfly

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