Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Weak Pete

Herb on Sun June 27, 2010 7:04 AM User is offline

Year: 2001
Make: Peterbuilt
Model: 379
Engine Size: Cat
Refrigerant Type: R134-A
Ambient Temp: 82
Pressure Low: 42
Pressure High: 110
Country of Origin: United States

Truck came in blowing cool, not cold air. Recovered 2.5 lbs, should hold 5.5 pounds. High side shraeder leaking badly, replaced it, no other leaks. OT clean. Holds 10.1 ounces oil, added 2 ounces BVA100 w/dye. Pulled deep vacuum for 1.5 hours, recharged to spec. Ambient 82F. Vent 70F. I believe it's a weak compressor, no noise or other issues. Something odd that worries me...the truck has an electromagnetic engine fan clutch that I toggled ON while charging, after full charge I turned it OFF to see if pressures would rise as expected. Nothing. Is this normal?? Tim, I will be calling you tomorrow for parts, I have all the numbers for truck and Chinese Sanden clone. Thanks everybody, Herb.

bohica2xo on Sun June 27, 2010 2:44 PM User is offline

It sure looks like a worn out compressor. an '01 Pete has what, 900,000 miles on it?


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Herb on Mon June 28, 2010 6:47 AM User is offline

I never bothered to check the mileage, it had a "N.E.W." (brand name) chinese clone on it. Bohica, any clue why the pressure didn't rise when I cut off the main fan?

ice-n-tropics on Mon June 28, 2010 1:46 PM User is offline

As you probably know the electric clutch on the engine fan can be engaged by water temp as well as A/C discharge pressure.
With the engine fan disengaged and cardboard temporarily blocking the condenser air flow, if the discharge pressure reaches 350 - 375 psi then compressor is OK (with 90% confidence level).
5.5 lb of R-134a would be for sleeper auxiliary A/C truck configuration.
A 91MY model probably has had 5 or more compressor changes. If A/C system was never flushed, then oil quantity is extremely high. OEM comp comes with 300 cc (10 oz.) of lube inside. 50+ oz of oil will not result in cold louver temp.
Since a/c was half charge, the accumulator probably contained 3+ oz of oil at that moment because the R-134a was highly superheated and did not wash oil out of the acc.
2 oz. of added dye oil adds to an oil overcharge cooling loss.
Of course, refrigerant suction pressure data would help.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Mon June 28, 2010 at 1:56 PM by ice-n-tropics

Herb on Mon June 28, 2010 2:26 PM User is offline

Thank all of you for the replies. Ice, I left the fan off, it was not engaged by the thermostat, barely turning, for about 30 minutes with no change in pressure whatsoever, I left the connectors open . If there is too much oil, wouldn't pressures be higher? Is it possible to "over-cool" the condenser? Low pressure was 42, I don't understand what suction pressure is. I'm confused with your answer. No insult , I just don't know what to do next. Was going to order new compressor and accumulator from Tim (emailed him this morning). I will have the truck only one day next week and need to have the parts in hand if that is what the problem is. And yes, it is a sleeper, forgot to state that in original question. Thank you, Herb.

Herb on Mon June 28, 2010 2:46 PM User is offline

Also, there was a lot of refrig oil the firewall and frame from the leaking high pressure fitting. Added 2oz just to be safe, realize now that could have been a mistake. Thanks again, Herb

ice-n-tropics on Tue June 29, 2010 1:12 PM User is offline

OK, low pressure =42=suction pressure
Excessive oil in a Pete A/C will not cause much notable overpressure on high side because condenser is so oversized, for Petes with tall condenser with big face area.
Earlier Pete's had a low condenser mounted below the air cooler. When Pete changed to the tall condenser (forward of the air cooler) they had a problem with rapid, nuisance cycling on day cab apps , their fix was to eliminate 1/3 of the tubes in the condenser to lower the cond heat dissipation capacity and R-134a charge amount.
If a accumulator is removed immediately after running then the oil taken out of the system that is stored inside the acc. is 3 to 7 oz for a low charged system instead of the full charge normal of 1 to 2 oz stored inside the acc.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Herb on Tue June 29, 2010 1:31 PM User is offline

Should I remove the old accumulator, drain the oil, then replace and recharge to check to see if pressures come up? Thanks, Herb

ice-n-tropics on Tue June 29, 2010 3:50 PM User is offline

That is a good question,
We do not know for sure if the A/C is overcharged with oil
Low oil would hurt comp durability
Accumulators are built with oil trap, therefore hard to drain out 1/2 of oil that is in acc.
Only sure service for correct oil charge is the flush system, drain comp, replace acc and then charge w/ 10 oz oil inside comp.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Herb on Tue June 29, 2010 4:22 PM User is offline

Ice, I concur, gonna fix it right and replace compressor and accumulator, change o-tube, flush with my HEACAT system, vacuum the hell out of it, oil it and charge. I didn't think to look, is the condenser a parallel flow? I still don't understand why the pressures didn't change at all. I'm a simpleton, at least that what my wife calls me...when she's in a good mood. Thank you, Herb

Herb on Tue June 29, 2010 4:50 PM User is offline

I sniffed all around the condenser with my Yokagama , but didn't think to look at it closely, out in sun,metal very hot, also took off the gauges and checked them against my F350, normal and Murphy go way back. Made sure they were back "in communication" with Pete. I assumed, yeah I know, at that year wouldn't be PF, hope it can be flushed. Thanks again, Herb

Herb on Tue June 29, 2010 5:37 PM User is offline

Just talked to my friend, condenser is serpentine, can be flushed. Whew!

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.