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need help 20+ years exp and banging head

kiaman5 on Fri May 11, 2012 5:29 PM User is offlineView users profile

Year: 1955
Make: chevy
Model: panel truck
Engine Size: 350
Refrigerant Type: 134
Ambient Temp: 85
Pressure Low: 20
Pressure High: 160
Country of Origin: United States

I have an aftermarket system and can't find an orifice or expansion valve. I put in a new compressor and took the guys word it worked before, even though when I went to do the orifice it wasn't where I thought it should be. So I get cool air and no low side pressure with the drier freezing up at times. I have done everything but tear the dash apart, and the reason I haven't done that yet is because the roof air and the dash air split right in front of the condenser, so if the valve or tube is in the dash it would only regulate the front air and not both. The lines are definitely made and not part of a kit I can tell by the welds. The spot that looks like it would accept an orifice does not fit any I have found. So, in basic language, the high side comes off the comp. and goes into the condenser. It comes out of the condenser and splits right there by the core support. That is where I think it looks like the orifice was supposed to be but there are no crimps in the line and nothing I can find fits properly. (small side has to go towards the evap, right?). So the high side splits there which is very far away for either evaporator. Splits there and goes in to both evaps (I pulled the roof air down and there is no exp valve). Then comes out of both evaps and reconnects under the right fenderwell, into the drier, and back into the compressor. Did they make the lines wrong??? Am I missing something here??? There has to be a metering device. I think I have spent so long on it I tried the net to just to ease my mind. Any help i9s appreciated.



TRB on Fri May 11, 2012 5:36 PM User is offlineView users profile

Do you have an drier or accumulator?




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Metal Man on Fri May 11, 2012 8:50 PM User is offline

The only Chevy truck I've done AC work on in my short career was a CCOT system. It had an accumulator and orifice tube.It was a 93 model best i remember. The orifice tube was located at the exit of the condenser. Just remove the bottom line from the condenser and there it was.

Another way to locate it would be feel for a sudden( hot to cold) temperature change in the lines.

I'm still a rookie at AC work so the pros might have a better way.

mk378 on Sat May 12, 2012 12:43 PM User is offline

A CCOT system is based on stopping the compressor before the low side gets low enough to cause freeze-up. The pressure switch is usually mounted on the accumulator. Or a variable displacement compressor could be used.

A common misconception is that a TXV is designed to regulate the evaporator to a specific temperature. They do not do that. The TXV tries to get the evaporator as cold as possible given the other conditions in the system. Some other part has to act to prevent freeze-up.

But aftermarket systems are almost always TXV. Dual evaporators would have two metering devices. In factory CCOT dual air, the dash has a OT and the rear evaporator a TXV.

bohica2xo on Sun May 13, 2012 6:44 PM User is offline

There has to be an expansion device for each evaporator. There is no way it ever worked the way you describe it.

The best solution is to add two TXV's to the system, one at each evaporator.

What sort of evaporator is in the dash? Something out of another car?

Post some pics if you can.


"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.

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