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Old 06-11-2018, 10:24 AM   #1
Shtudwn
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1976 K20 a/c Recharge Port

I have a 1976 K20 that appears to have been converted to 134a. Well at least that is what the little sticker on the Accumulator/Drier says.

There are two threaded schrader type ports on the Accumulator/Drier and one in-line of one of the hoses. None of them have the 134a quick-connect adapter. The in-line fitting has the two-wire switch connected to it.

Where do I attempt a recharge of the system? I have an adapter but the three locations gives me two too many options! haha

Thanks.
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Old 06-11-2018, 11:21 AM   #2
70GMCer
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Re: 1976 K20 a/c Recharge Port

Do they look like this?
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Old 06-11-2018, 01:05 PM   #3
100%Chevy
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Re: 1976 K20 a/c Recharge Port

The switch on the in-line fitting should be moved to one of the fittings on the accumulator/dryer.
Then,you use the other fitting on the accumulator/dryer for the low pressure guage line connection and the in-line fitting for the high pressure guage connection.
You can get the 134-a adapters at the auto parts store for the correct connectors for the 134-a quick connects.
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Old 06-11-2018, 01:36 PM   #4
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Re: 1976 K20 a/c Recharge Port

Charging is done on the low side port
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Old 06-11-2018, 04:27 PM   #5
Shtudwn
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Re: 1976 K20 a/c Recharge Port

Sorry everyone, I am having a heck of a time posting pictures which I think would make this whole thing much more clear than my bable!

Last edited by Shtudwn; 06-12-2018 at 10:16 AM.
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Old 06-11-2018, 10:42 PM   #6
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Re: 1976 K20 a/c Recharge Port

Assuming your 76 AC is like my 75's, the lower port on the fitting with the switch is the high pressure side. Don't fill there. Also, don't move the switch, it is your HIGH pressure cutout that will turn off the compressor if the pressure is too high.

The proper fill port is the blue one in 70GMCer's pics.

If you have a gauge, see if any pressure is left. If not, you will need to vacusuck it to clear out any air before attempting to refill.

No clue on how to test if the stuff inside is R-12 or R-134 or something else. Folks have been known to use propane-butane mixes as an R-12 substitute.

Possible the second port in your drying is for a LOW pressure cutout switch. Mine has a thermostat in the evaporator housing that cuts the compressor if things get too cold. I think later systems went to a low pressure cutout.

If you attempt to fill it, I suggest making the first can one of the combo leak detect/sealant cans and check for leaks before trying to fully fill.
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Old 06-12-2018, 10:18 AM   #7
Shtudwn
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Re: 1976 K20 a/c Recharge Port

Name:  1976 AC Ports.jpg
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yes!!!!!
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Old 06-12-2018, 10:55 AM   #8
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Re: 1976 K20 a/c Recharge Port

You can check out my thread on a similar issue.

http://67-72chevytrucks.com/vboard/s...d.php?t=763399

Im NOT an expert but I think that accumulator is for a R134 system that would have had a high pressure cutoff switch on that additional port. R12 systems originally wouldn't have that. You would typically use the port facing towards the front of the truck. If you are trying to use R134 you may need adapters to use on your lower liquid line and the front port on the dryer. I think..
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Old 06-12-2018, 09:36 PM   #9
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Re: 1976 K20 a/c Recharge Port

Lower port in your pic is the high pressure side. Don't fill there.

Fill using one of the upper ports.

I would borrow/buy a gauge if you don't have one and check for existing Freon.

I still have R-12 in mine but most of the threads on conversion mention you REALLY want a good vacuum before adding R-134. Apparently, it isn't as tolerant of a little air as R-12 is. If there is already some and you are just low, shouldn't need to vacuum first. Also, don't use the amount listed on an R-12 compressor, 134 systems use less.
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