![]() (5) Make sure re circulation function is working. Getting good air flow through the condenser is critical, especially if you want good performance when the car is sitting still. (4) Use an electric radiator fan with a shroud. Air blowing around under the dash is not as effective as air blowing at the passengers. You can use household self-adhering weatherstripping foam to replace the original seals if they are not working. You can run this down to the frame if you want to ensure best ground. The fan motor mounts to a fiberglass, non conducting box on the firewall, so it needs a dedicated ground wire to the body of the fan. (2) Make sure your fan is getting a good dedicated ground. ![]() If it doesn't work, your blower motor will not have the maximum speed. This relay is located on top of the AC box and it is only turned on when the fan switch is set to high speed. ![]() (1) Make sure the high speed fan relay is working properly. Other things you can do to maximize performance: If you use the original condenser, pressures will rise on the high side of the system and it may not be able to keep up with cooling demand in high ambient temperatures, again leading to higher vent temperatures. Get the largest parallel flow condenser that you can fit and get good air flow. The original condenser is a tube and fin design which is much less efficient at heat transfer and it becomes a major limiting factor, especially when using r134a. (3) The condenser should be replaced with a parallel flow condenser. The pressure needs to be lowered to abot 25psia. This means if you don't adjust the POA valve, your evaporator will be warmer and therefore the air coming out of your vents will be warmer too. The original pressure setpoint (29psi) keeps R12 just above freezing, but 134a at the same pressure will be at a higher temperature. (2) The POA valve needs to be adjusted so the pressure in the evaporator is correct to keep r134a near freezing. The result is less cooling capacity, leading to higher temperatures out of the vent. When using an R12 TXV with R134a, the evaporator will not be fully utilized because the refrigerant will be superheated more than necessary. Most replacement TX valves are already setup for 134a, but if you have an original TX valve you should replace it. (1) The expansion valve (TX valve) needs to be appropriate for 134a due to different superheat temperature needs. There are a few important thing to consider when using the factory AC and 134a The system and it's operation are fairly simple, but there are some pitfalls even if the components are in good working order. I'm a mechanical engineer who studies heat transfer / heat pump / AC systems and this factory AC system design and operation fascinates me quite a bit. I'm happy to answer any questions you have. I'm going to copy-paste some useful information below regarding how to get the factory system working well, since I have gone through this on my '70. Many folks swap them out for a newer Sanden compressor which will also work. They are enormous and heavy, but also known to be relatively bullet proof. The original compressor is a Frigidaire A6.
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