AC High/Low Side Help - Team Camaro Tech
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post #1 of 7 (permalink) Old Jul 29th, 07, 03:04 PM Thread Starter
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Question AC High/Low Side Help

I am trying to convert my AC system from R12 to R134. I don't know much about AC systems and this is not a stock AC. I want to be sure I'm doing this correct.

I have attached a photo where you can see two valves on the back of the compressor I believe the value on the far side of the compress is the low side but I'm not sure. Coming out of the firewall you can see on more connector. I have a three hose gage set and not sure where to hook up each hose. Could someone point me in the right diretion?

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post #2 of 7 (permalink) Old Jul 29th, 07, 04:16 PM
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Smile Re: AC High/Low Side Help

The port near your evaporater should be your low side. Blue hose of your gauges. The port on the compressor that a hose runs to your condensor (in front of the radiator) is your High side. Red hose of your gauges. Hope this helps.

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post #3 of 7 (permalink) Old Jul 29th, 07, 05:04 PM
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Re: AC High/Low Side Help

Both of the ports at the compressor is where I would hook in for the best readings, they should be marked with a S for suction(low side where the blue hose connects) and an A for discharge(high side where the red hose connects). If they aren't marked then as TJS69 said the hose that goes to the condensor is the high side. You do know that if you are changing to 134 that you need to flush the oil out of the entire system becasue the different oils used for each refrigerant are not compatible with one another. Why are you switching?
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post #4 of 7 (permalink) Old Jul 29th, 07, 06:05 PM Thread Starter
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Re: AC High/Low Side Help

I must have a leak because I am blowing warm air. I can't buy R12 so I thought I'd switch to R134 then I could refill the system and add a stop leak additive to see if it would work.

But, after reading a little more about whatís involved, I may not attempt it. I guess Iíll bite the bullet and take it to a local AC shop. I just hate leaving my car with anyone. My fear is Iíll pick it up with bald tires and hell beaten out of it. But, what can ya do.

Thanks for the info....
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post #5 of 7 (permalink) Old Jul 29th, 07, 06:38 PM
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Re: AC High/Low Side Help

both sides are different.threads. small and thicker the r134 will bolt up to it if bought conversion kit. and red or blue caps are on it.
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post #6 of 7 (permalink) Old Jul 30th, 07, 03:49 AM
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Re: AC High/Low Side Help

The valve on the left of the picture, evaporator pressure, is for a third gauge, or use the blue low pressure gauge and swap back and forth from the suction side of the compressor.

The smaller valve on back of the compressor is the high side. You would have to get an adapter to adapt from 1/4 inch fitting, low side size, to 5/16 inch fitting, for the red high side gauge.

Be sure you get an elder HVAC tech who has worked with POA system. POA keeps the evaporator between 30-35 PSI, suction side on compressor may go into a vacuum if working properly. Most HVAC techs are too young to know, or only worked with residental/commerical A/C and know nothing of a POA or STV from Ford. Not saying they couldn't learn and mentor others, but, POA is a type evaporator regulating valve.

If you converted to R-134A, major change. POA valve would have to come out, new hoses, change compressor oil and receiver, and convert to orifice type system, not that hard, as in late model design after 1988. Plus a system flush of every component. Labor would be your biggest expense.

Just my thoughts.

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Last edited by Everett#2390; Jul 30th, 07 at 07:48 AM. Reason: Had the wrong size for the high side, Thanks, Tom!
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post #7 of 7 (permalink) Old Jul 30th, 07, 07:34 AM
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Re: AC High/Low Side Help

The R134a Port on the POA Valve is your Low pressure (suction) fitting. You check the low side pressure there and evacuate(place under a vacuum) and charge the system from that port.

At the compressor. The High Side port is the one directly under the discharge hose running from the compressor to the Condenser. It has a Larger quick connect fitting on it now and is the proper Ra high side fitting.
The threaded fitting under the suction hose at the compressor needs a cap placed on it and left ALONE. It is an R12 fitting, as were the other two fitting described above but have had R134a fittings added to them.

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