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SCRATCHING MY HEAD AND WIPING SWEAT

darrenmcentire on Mon July 12, 2010 12:32 AM User is offlineView users profile

Year: 2007
Make: PETERBILT
Model: `379
Engine Size: 475 CAT
Refrigerant Type: 134A
Ambient Temp: 100+
Country of Origin: United States

HI EVERYONE.
I JUST GOT THIS TRUCK IT'S A 2007 PETERBILT 379 WITH A 475 CAT. ENGINE. 84" SLEEPER. WHILE DOING THE INITIAL CHECK OVER AT THE DEALERSHIP THE AIR CONDITIONER WORKED FINE. BUT AFTER GETTING OUT ON THE INTERSTATE AND PULLING A LOAD WITH IT THE A/C STARTED TO BLOW ONLY HOT AIR. BOTH IN CAB AND IN SLEEPER. I TURNED OFF THE HEATER LINES TO THE CAB AND BUNK AT THE VALVES ON SIDE 0F ENGINE. HELPED BUT ONLY A LITTLE. TEMP AT VENT WAS 96 IN FRONT 105 IN REAR. AMBIENT TEMP WAS 99. AFTER SUFFERING FOR SEVERAL HOURS I STOPPED FOR A BREAK AND WHEN I RESTARTED THE TRUCK IT WORKED FINE FOR A FEW HUNDRED MORE MILES..THEN REPEATED THE EARLIER PATTERN....ENGINE FAN OVERRIDE/MANUAL SWITCH WOULD CAUSE IT TO START TO WORK FOR SHORT PERIODS.....I TOOK IT TO SHOP AND THEY REPLACED ACCUMULATOR/DRIER AND A FILL VALVE . WASHED OUT THE CONDENSER ON FRONT OF RADIATOR AND BOTH OF THE DUST/POLLEN FILTERS. THIS CURED THE PROBLEM IN THE CAB.
BUT!! THE SLEEPER BLOWS ONLY WARM AIR. THERE IS A SEPARATE CONDENSER FOR FRONT AND REAR AND BOTH SHARE COMPRESSORS. I ASSUMED IT WAS A DIVERTER DOOR NOT FUNCTIONING AND TOOK BOTH ELECTRONIC ACTUATORS OFF AND WHILE OPERATING THE TEMP CONTROL OBSERVED THEM BOTH WORKING PROPERLY. I INSPECTED THE LINES RUNNING BACK TO SLEEPER (HI LO PRESSURE ) THEY ARE BOTH AMBIENT TEMP. THE LINE THAT RUNS TO THE CAB GETS VERY COLD AND IS TEE CONNECTED TO THE SLEEPER LINES WITH NO EVIDENT VALVES THAT COULD BE CLOSED.
WHAT SHOULD I DO NEXT? I AM LOADING IN THE MORNING GOING TO EAST TEXAS AND THEN SOUTH FLORIDA....AND WANT TO AVOID ANOTHER SHOP VISIT IF AT ALL POSSIBLE..

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DARREN G MCENTIRE

mk378 on Mon July 12, 2010 1:58 PM User is offline

When neither one is cold, open the hood and see if the compressor is engaged.

If cab is cold but sleeper not, it could be because of a solenoid valve in the liquid line to the sleeper TXV intended to stop the refrigerant flow when the sleeper fan is off. If it's not that the sleeper TXV could be clogged/bad, or the system undercharged.

ice-n-tropics on Mon July 12, 2010 5:14 PM User is offline

Quote
Originally posted by: darrenmcentire
HI EVERYONE.

WHILE DOING THE INITIAL CHECK OVER AT THE DEALERSHIP THE AIR CONDITIONER WORKED FINE. BUT AFTER GETTING OUT ON THE INTERSTATE AND PULLING A LOAD WITH IT THE A/C STARTED TO BLOW ONLY HOT AIR. BOTH IN CAB AND IN SLEEPER. I TURNED OFF THE HEATER LINES TO THE CAB AND BUNK AT THE VALVES ON SIDE 0F ENGINE. HELPED BUT ONLY A LITTLE. TEMP AT VENT WAS 96 IN FRONT 105 IN REAR. AMBIENT TEMP WAS 99. AFTER SUFFERING FOR SEVERAL HOURS I STOPPED FOR A BREAK AND WHEN I RESTARTED THE TRUCK IT WORKED FINE FOR A FEW HUNDRED MORE MILES..THEN REPEATED THE EARLIER PATTERN....ENGINE FAN OVERRIDE/MANUAL SWITCH WOULD CAUSE IT TO START TO WORK FOR SHORT PERIODS.....

BUT!! THE SLEEPER BLOWS ONLY WARM AIR. THERE IS A SEPARATE CONDENSER FOR FRONT AND REAR AND BOTH SHARE COMPRESSORS

Darren,
initially the computer probably sensed undercharged R-134a and disengaged the clutch to avoid compressor internal damage so that you would get it serviced. When you restart the computer is reset. Hopefully your service man found the leak.
You say you have 2 condensers and 2 compressors all inter-connected? Does the sleeper get cold when the CAT is running?, or... is it hot when only the auxiliary A/C is on and the CAT is off?
The 2 A/C systems need to be separated so that the compressors will have the proper oil return for acceptable life.
hotrodac (Texas)



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

Edited: Mon July 12, 2010 at 5:21 PM by ice-n-tropics

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