AIr Conditioning Recharging

[Roger S.]

My late '73 AC compressor is equipped with a '74 inlet/outlet block. This block has the schrader fitting located on the left side port, as viewed from the back. This port I believe is the suction line to the compressor from the VIR. The right block port goes to the front of the radiator to the condenser. The VIR has a schrader fitting on the top. Both fittings are the same thread. As I understand the AC system the high pressure side, many years ago, had a smaller schrader fitting so as not to get the high and low pressure connections mixed up.
Anyway the question at hand is how to I measure the high pressure side of the refrigerent system, or is that even necessary? I have been told to measure both the high and low pressures to ensure that the system is working properly.
Roger

[Jack H.]

Re: AIr Conditioning Recharging

Corvette's Four Seasons A/C system is a strange hybrid.... The compressor setup was 'borrowed' from the Chevy A/C system (the dealer installed under dash 'box' as well systems used on Chevy pickup trucks) and compressor displacement is somewhat less (smaller cabin to cool down) then conventional Four Seasons A/C systems used in tradition Chevy passenger cars. The dealer add-on system had 'works in a drawer' with the evaporator and blower/distribution components being mounted under dash. Hence, there was no way to access Schrader valves for re-charge/monitoring with everything under the dash and the valves moved to the compressor manifold for service access convenience.

In the Corvette version of the system, a conventional Harrison 'air box' is mounted to the firewall containing expansion valve, evaporator, Etc. So, both high and low pressure Schrader valves ARE mounted there in addition to the valve(s) that 'live' on the compressor manifold. This gives multiple access points (as well as multiple valves to leak/and verify).

Your copy of the Chevy Chassis Service Manual will document where the valves 'live' and which is the high vs. low pressure side.... If the system is fully discharged, my recommendation is to 'gut' it and shotgun replace ALL of the original Schrader valves & attaching line gaskets with the best commercial refigeration grade components you can get (might cost you a whooping $10 more than the original automotive grade components used) and be sure to read/OBEY torque specs at the various connection points! Over tightening a refrigeration gasket can be just as bad as under tightening it from a long term system integrity standpoint!

[Roger S.]

Re: AIr Conditioning Recharging

In the '73's and later the expansion valve is incorporated into the VIR, valves in receiver. This only has a low pressure vapor schrader valve and is on top. According to the '73 AIM the high pressure fitting was on the compressor block on the right side for the line going to the condenser. For 1974, it appears due to failures in the high pressure hose, being too close to the exhaust manifold, the high pressure valve was put in the hose by the fender and the low pressure tap was on the VIR and on the compressor left side block.
Since it appears like I don't have a high pressure tap I am wondering do I really need it. My system is not empty and I am just going to "top it off".
So I guess I add some refrigerant until the low pressure side is up to 32 psig and the vent temperature is around 35F.
Roger

[Harmon C.]

Re: AIr Conditioning Recharging

Roger I don't think 73's had a high side and have used only the low side and checked the vent temperature to top them off. Lyle

[Jim T.]

Re: AIr Conditioning Recharging

Roger does your 73 have a sight glass on the dryer? On my 70 I charge it until I get a clear sight glass.

[Craig S.]

Re: AIr Conditioning Recharging

My 74 has a sight glass in the line on the fender, in a block. As you say, charge till clear...Craig

[Harmon C.]

Re: AIr Conditioning Recharging

Jim I never have seen a sight glass on a 73. I like them top down with 55 air. Lyle