Old 05-22-2023, 11:57 PM
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Tuske427 Tuske427 is offline
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Default 1969 GTO factory AC questions


new '69 GTO owner here, and I had a couple of questions about the factory AC system that I haven't been able to find info on:

1- is there a "Max AC" setting? It seems ( and correct if I'm wrong) that the INSIDE setting is a dashboard vent function only, and the AC setting operates both the dash and the feet vents. neither seem any colder than the other.

2- if there isn't a Max AC setting, is it possible to make one? ex: close off an outside vent for air inlet?

or is there another way to improve the AC system on these without having to gut it and use a vintage air, etc. and yes, new USA made compressor, freshly recharged system so it should be working as originally designed. Yes, it works OK, but not as well as I thought it might. I have also sealed off the ducting with glue and HVAC tape (not duct tape) under the dash to ensure I'm getting all the air possible to the vents.


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Old 05-23-2023, 12:53 AM
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hgerhardt hgerhardt is offline
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"Inside" means recirculated air, which is the same as "max AC" in later cars. Not sure if the '69 has a water valve, but if it does, "inside" should close that valve, as well as close the flap which lets in outside air.

There should not be much, if any, air to the feet unless "heat" or "defrost" is selected. I suspect the heater outlet dashpot (vacuum-powered actuator) has sprung a leak or the vacuum valve which is what the dash selector actually operates has a leak.

As to cooling performance, there's so many variables to get right. Which refrigerant? If R-134a, you'll get better performance with a parallel-flow condenser. If 134a, is the POA valve calibrated for that? Is there even one in there or was it replaced with a cycling clutch tube? What are the pressures during operation and at what rpm's? Do they correspond to the chart?

Old 05-23-2023, 03:39 PM
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I recall 45 years ago driving my girlfriends a/c equipped '69 hardtop in the summer at the Jersey shore. It would blow so cold vapor blew out the vents. Later I had a '72 TA and it was charged with R12 and my girlfriends would complain about how cold it was inside the car. Now my '69 GTO convertible has a factory system I restored from new and used parts and a cycling clutch tube. It has R134. Its 'adequate' for here in Florida but not as good as I recall the old days. I have a couple dozen cans of R12 and 1 15lb tank; when I get the chance I'm going to have it switched back. It has the newer high efficiency condensor too. I had a '87 Cutlass with a R12 system that would have condensation running down the sides of the windows outside. When I had to switch it to R134 it was only cold when the car was moving. Any time sitting in traffic it would not so slowly get warm. Only one little thing to consider is the fins on the 'hamster wheel' fan get clogged with dirt and lessen efficiency over long periods.

Old 05-24-2023, 01:51 AM
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I was listening to Rush Limbaugh years ago when he mentioned his old 69 Lemans had the best AC of any car he's ever owned.

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Old 05-24-2023, 03:18 PM
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I agree that a factory AC on a 69 GTO should be icy cold if you want. If you are not getting air that cold (as opposed to zero cooling) there are a few possible causes.

First as mentioned is the refrigerant, when GM switched the R134 in 94 they increased the size of the evaporators and condensers about 30% to compensate for the weaker thermal capacity relative to R12. So if you are running R134 it should still be fine for all but the worst days but definitely not up to factory spec.

Second is insufficient refrigerant level.

Third is a malfunction of the hot water cut off valve. This valve is vacuum controlled and it functions when the temperature slider is in full cold position to the far left. It cuts hot engine coolant flow to the heater core when activated

Forth is malfunction or bad adjustment of the flapper doors which are cable controlled by the temperature slider

Fifth is decades of filth blocking the evaporator in the dash, this limits both airflow and heat transfer resulting in lower vent flow and warmer temperatures.

Lastly the evaporator in front of the radiator may also be blocked by dirt and grime reducing heat transfer.

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Old 05-24-2023, 11:25 PM
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thank you, everyone, for the great replies. I must admit I know next to nothing about AC so I need to read up to even understand what everyone is speaking about in the replies. So for the moment I'll add some pics and hopefully some of these questions can be answered.

what little I do know is the following: new compressor, and R134 refrigerant level should be good (system was checked for leaks). less than a month old.
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Old 05-25-2023, 07:51 PM
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Mark Simiele Mark Simiele is offline
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Good luck with your a/c and keep the R12 too.

Knowing what I know now I would have never switched over to R134 when my car was restored 20 years ago. It blows very cool bit not freezing like R12 cars do as others have said on this post. Many a veteran ac tech have told me R12 was a far superior refrigerant and they were correct.

Unfortunately I listened to all the hype that R12 was going to be very difficult to find and very $$. It isn't cheap but I find the prices have come down since then. There is also still plenty out there for sale and been accumulating it when I can find it for a good price which is still possible.

One day its going to get changed back over and when the day comes for the Bonneville to get restored that will remain an R12 system.

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