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1970 Nova LS Swapped
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Discussion Starter #1
For anyone interested in learning how the late 60s / early 70s GM Frigidaire factory AC system works, I made an in-depth 30min video explaining how it all works in my 70 Nova. The system is the same as what's used in first gen Camaros, with many of the components shared.

In the video, I explain how the factory AC system operates and what's needed to update the system for R134a.

Explanation of controls 0-10:20
Driving test 10:20-12:55
Underhood components & purpose 12:55-25:36
Whats needed to use R134a 25:35-33:32
Factory AC vs aftermarket 33:32-end

[video=youtube_share;jNUb-GDWz4Y]

I also made a few videos to help with flushing the evaporator and testing/adjusting the POA valve:
Flushing the evaporator: https://youtu.be/vMpsEwh7Uqg
Testing the POA valve: https://youtu.be/PhWW7hD9-Yw
Adjusting the POA valve: https://youtu.be/B95_q7Z8DIE

I hope these are helpful to others!
 

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Discussion Starter #2
Here are a few important thing to consider when using the factory AC and 134a
(1) The expansion valve (TXV valve) needs to be appropriate for 134a due to different superheat temperature needs. Most replacement TX valves are already setup for 134a, but if you have an original TX valve you should replace it. When using an R12 TXV with R134a, the evaporator will not be fully utilized because the refrigerant will be superheated more than necessary. The result is less cooling capacity, leading to higher temperatures out of the vent.
(2) The POA valve needs to be adjusted so the pressure in the evaporator is correct to keep r134a near freezing. The original pressure setpoint (29psig) keeps R12 just above freezing, but 134a at the same pressure will be at a higher temperature. 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 pressure needs to be lowered to about 25psig. I have a video of doing that linked above
(3) The condenser should be replaced with a parallel flow condenser. 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. Get the largest parallel flow condenser that you can fit and get good air flow. 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.

Other things you can do to maximize performance:
(1) Make sure the high speed fan relay is working properly. 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. If it doesn't work, your blower motor will not have the maximum speed.
(2) Make sure your fan is getting a good dedicated 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. You can run this down to the frame if you want to ensure best ground.
(3) Ensure all duct work is sealed. You can use household self-adhering weatherstripping foam to replace the original seals if they are not working. Air blowing around under the dash is not as effective as air blowing at the passengers.
(4) Use an electric radiator fan with a shroud. Getting good air flow through the condenser is critical, especially if you want good performance when the car is sitting still.
(5) Make sure re circulation function is working. When set to "Max", the factory AC has a vacuum valve that operates a re circulation flap in the passenger footwell area as well as one on top of the cowl. If it's working propertly, you will hear more fan noise from the passenger footwell area when the AC is set to "max". If it's not working properly, make sure the vacuum lines are connected to manifold vacuum and that the duct operators are working.
(6) Make sure the heater shutoff valve is working. There should be a vacuum-operated shutoff valve located on the inner fender that stops the flow of coolant to the heater core when the AC is set to max.
 

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Hey Mr Bandit, Great Info. Ty

I have an R-12 qustion. New Restoration, factory a/c system. Is the oil used with an R-12 system and the oil used in a 134a stsem the same / interchangable? I'm asking because im not sure how difficult it may be to find and old stock of the old 12 oil bottles. would you know if there still available? I have pleanty R-12 freon. Also, is there any modern upgrades that should be considered for the factory A6 compressor?
 

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Discussion Starter #4
Originally th A6 compressor with R12 would have used a mineral oil but for R134a you want to use a PAG oil. According to the site below you should use PAG 150. My FSM calls for 11oz. I am not sure what the process is for flushing the old mineral oil out of the system.

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As far as a compressor "upgrade" I know a lot of folks put Sanden compressors on these but I think that's primarily to get a more compact, lighter unit. From an AC performance standpoint I don't think it's an upgrade unless the original compressor is worn out.
 

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Thanks for the heads up on the different oils. Are you also saying a virgin sytem should have 11oz of oil? That sounds like allot?
 

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Discussion Starter #6 (Edited)
11oz is the stated capacity per my 70 Nova factory service manual. I assume that is for a new/dry system. I recommend getting a FSM for you car - there is a lot of great info in there.

Hopefully others will chime in on the use of the A6 because I honestly do not have experience with using one.
 
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