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67 Corvette help

jrs396 on Sat June 05, 2010 10:34 AM User is offline

Year: 1967
Make: Chevrolet
Model: Corvette
Engine Size: 427
Refrigerant Type: R12
Ambient Temp: 82
Pressure Low: 70
Pressure High: 200
Country of Origin: United States

Hi all,
I am helping a friend with his car,Every year the system always needs alittle hit of gas to clear up the site glass
and cool correctly.This year I noticed after adding alittle R12 the car was not cooling properly and the readings at idle
are 70 low side at POA fitting and 200 High side at compressor fitting.I raised RPM to 2000 and the readings went to
60 on the low side and 225 on the high side.Can someone point me in a direction on where to start my diagnosis.
Center outlet does not change and stays at 55 degrees.

The factory manual is alittle lacking on info for diagnosing A/C system,only found a test for the expansion valve.
I guess I will start there.

Thanks
Ken

NickD on Sat June 05, 2010 5:24 PM User is offline

Something is sticking, POA should hold the low side at 28.5 psi, that is its purpose.

Also having a bit of fun with my friends 65, has an ammeter instead of that Bat warning lamp, but has the dual relay voltage regulator. Recall GM used just the voltage regulator for this applications, found an old schematic, F to field, ignition switch to pin 3, you get ground for free by mounting it. With the stator relay added, pin 3 on that goes to a normally open contact, no wonder why is alternator will not start up, but works perfectly in my test bench.

Only purpose of that stator relay is to switch on or off that bat light and doesn't do it very well, only take 2.68 volts to energize it which translates to about a five volt output, not quite enough to charge a battery. I swear I have seen those VR only regulators, but can't find one on the web, anywhere. If I manually close the stator alternator fires right up, but just have the regulator and the alternator, not the car. Use to have shop manual on this car, when they were four bucks including postage. Yeah, GM never said much about AC back then, just buy a charging station and all will be okay.

My friend is five years older than me, I am just a kid.

hjc149 on Sun June 06, 2010 1:19 PM User is offlineView users profile

hjc149 on Sun June 06, 2010 1:21 PM User is offlineView users profile

I agree. Sounds like the POA valve. I don't know if you can get the original type anymore or not.

Dougflas on Sun June 06, 2010 3:17 PM User is offline

while hooked up and rpm @1500, disconnect the blower motor lead. Low side should be at 28 to 32 with 30 psi optimal.

NickD on Sun June 06, 2010 8:19 PM User is offline

Thinking way back, GM never stated pressure readings, but wanted you to use a charging station to put in the correct amount of refrigerant. We got around that by simply charging while hand feeling the evaporator outlet until it got as cold as the inlet and the liquid line for pulsations that would disappear as the full charge was met.

Is possible this system is way overcharged so the POA can no longer regulate it. Using gauges on this compressor bypass system was tricky.

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