2001 Isuzu Rodeo Question AC pressures diagnosis

WILDFIRE11

MEMBER
2001 ISUZU RODEO
6 CYL
4WD
AUTOMATIC
97,000 MILES

Recently purchased so I'm not aware of the history, although I did buy it knowing that the A/C doesn't work. The system is an accumulator-drier, expansion valve system.
Hooked up guages, low and high side pressures both at zero.
Pulled vacumn to -30 Hg for 20 minutes, then shut off compressor and let sit for another 30 minutes. The needle remained dead on at -30 Hg, which surprised me, since I expected a leak.
Proceeded to add one can (12 oz.) R-134a to low pressure side. Started engine, ac on, fan on high. Jumped pressure switch and compressor clutch engages immediately, no noise or anything out of the normal, compressor seems to be working. Low and High pressures jump to 70, with compressor running and it then remains stable at 70 on both sides. At this pressure, the compressor now runs on its own continuously, although it can be activated on or off with the A/C switch on the control panel in the dash board, based on what is selected.
So my question is. What next? Could the 70 pressure (low and high) be solely from the can off freon, even though the compressor seems fully operational otherwise, or are these pressure a result of at least some compressor action? Also, the system seems to be open across the expansion valve or compressor, since there is no difference between the high and low side.
Any suggestions? Thanks

7 Replies

SATURNTECH9

MECHANIC
30,870 POSTS

First of all thank you so much for your donation. Equal pressure's on the high and low side usually mean's you have a bad a/c compressor. So you only put in 12 oz's of charge?Let me know.

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Monday, September 20th, 2010 AT 4:15 PM

WILDFIRE11

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4 POSTS

It wouldn't even take the full first 12 oz. Of charge. Once the low side pressure reached 70 and equalized with the high side at 70, I assumed that the pressures had all equalized with the pressure in the freon can and the system would then not draw in any additional freon. Normally, I would have expected the high side to slowly rise in pressure while the low side remained low enough to draw in freon from the can(s) until I reach the desired full charge to see how the system worked under full charge, but I can't draw in any additional freon.

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Monday, September 20th, 2010 AT 4:40 PM

SATURNTECH9

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You should have had the high side closed when you charged it especially with the engine running if the compressor came on and was working correctly if the high side manifold was open the charging can could explode. So with the compressor running the high and low side are equal?The low side is suppose to be 21-43psi and the high side should be 199-270 psi. If there equal at 70 psi with the compressor running then the compressor isn't doing much pumping. Try taping on the compressor with the compressor running and the gauge's hooked up and see if the pressure's change any.

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Monday, September 20th, 2010 AT 7:03 PM

WILDFIRE11

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4 POSTS

Sorry for a bit of delay. This morning - static pressure (engine off) - 40 high and low. Ambient temp - 55. Cranked engine, compressor clutch not engaged. Turned on blower fan to high, slid temp control to full cold, pushed a/c button and heard clutch engage. Compressor appears to be spinning. Both guages remain stationary at 40, regardless of engine speed.
Compressor continues to turn and nevers cycles off. Can engage and disengage the compressor manually using the a/c button on the dash, however several trys back and forth at different engine speeds from 1500 - 3000 results in no changes to either guage reading. Taping on the compressor also results in no change.
I guess the root of my question is while the compressor is obviously not doing anything, I wanted some second advise that I am not overlooking a stuck or restricted expansion valve (although the trouble does not match to normal stuck expansion valve troubles, open or closed), that I'm not missing a faulty switch or otherwise overlooking something simplier and more obvious before biting off a new compressor?
Thanks - John

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Tuesday, September 21st, 2010 AT 7:52 AM

SATURNTECH9

MECHANIC
30,870 POSTS

There is all the pressure chart's for diagnoses of bad pressure's.Your a/c system is about half full it hold's 1.5lb's.I also emailed you the chart's.