1955 Chevy Belair Factory A/C

[Dars55Belair]

New member here seeking help on my R-12 to R134a conversion. I am a novice when it comes to A/C systems. I’ve restored this historically significant Sport Coupe that was built with all power options and was one of about 600 cars that were sold to dealers to drive sales of accessories in early 1955. I’ve restored all major components of the system but changed the condenser to a new parallel flow design and added a freon pressure switch type dryer. The system was flushed and charged in a professional shop and was initially working and cooling to about 65 degrees F. Unfortunately after the engine warms up to operating temp the A/C system output temp rises to about 85 degrees.
The original design has an insulated evaporator/heater core enclosure mounted to the firewall in the engine compartment. I’ve disconnected the heater core in an attempt to reduce possible heat transfer from it. That didn’t help. I’m not sure what I should do next. Hoping someone here can help. Thanks, John

[Cusser]

The system was flushed and charged in a professional shop and was initially working and cooling to about 65 degrees F.

That's terrible !!!

[JohnHere]

First step is to record and post pressures at about 1,800 RPM using a pro-model Manifold Gauge Set, as well as the ambient temperature.

Does this car still have the original non-clutch fan and no fan shroud? Reason I ask is because it sounds like mainly a condensing problem (lack of airflow through the condenser).

[Dars55Belair]

Thanks for the responses. I built the system and then had a close friend who owns a repair shop vacuum and charge it. The pressures were 30 and 150 respectively at 85F. I’m using the 5 blade GM fan that was designed for a 1955 A/C car and have added a fan shroud.

[JohnHere]

Presuming the OE A5 compressor is up to snuff, the high-pressure side of the system is quite low at that ambient temperature, and the vent temperatures indicate that little to no cooling is taking place. Even though you've installed a PF condenser, fan shroud, and an OE 5-blade fan, which is designed to flatten out at cruising speeds to reduce drag and noise, the condenser still probably lacks good airflow across it, especially at low speeds.

It's sometimes difficult to get the refrigerant amount just right with classic-car conversions like this one. One of the ways to do that is to "sneak up" on the optimum charge—that is, continue adding refrigerant, one ounce at a time, while keeping an eye on both the pressures and vent temperature. As soon as you see the pressures and vent temperature start to rise above the optimum, stop charging at that point.

Depending on the condensing efficiency, you should see HS pressures of around 190-210 PSI and vent temperatures of 40-45°F at the aforementioned ambient of 85°F at about 2,000 RPM.

Adding an electric fan and sealing the gap between the condenser and radiator using foam insulation from your local home center probably will help cooling.

[Dars55Belair]

Thanks for all the good info. The A5 was restored by a reputable shop so I’m pretty sure it's working correctly. When I add the electric fan would it be best to just have a manual switch and run it full time while the A/C is on? I will try your suggestion about the charging and hopefully I can get in the 195-210 range. Thanks again

[JohnHere]

Sure, that's a great way to wire-in an auxiliary fan. You could even hide the switch somewhere if keeping the stock appearance is important.

Alternatively, you could wire it in such a way that the fan comes on automatically each time you switch-on the A/C.

[Tim]

Alternatively, you could wire it in such a way that the fan comes on automatically each time you switch-on the A/C.

Yep, and on a relay setup. Electric fan movement (forced air) when not engaged and is wired directly to the clutch circuit. Will cause feedback into the compressor clutch. Bye bye clutch coil.