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I have a 1978 Pontiac Firebird fully converted to R134a.

Customer Question
Prior mechanic installed new compressor...
I have a 1978 Pontiac Firebird fully converted to R134a. Prior mechanic installed new compressor with only the 3 ounces in the compressor. It takes 8 ounces. So, first compressor fried. I replaced the compressor (with the proper amount of PAG). But, I have 2 issues.
I can draw down a -30 vacuum and the vacuum holds if you come back in an hour and look at the gauges. But, if you leave it over night, the vacuum does not hold that long. It goes from -30 to 0 sitting over night.
It will not take a charge no matter what I do. I've tried 3 different sets of manifold gauges. 2 different can piercing handles. 2 different brands of refrigerant. The can does not have enough pressure to push any refrigerant in and the AC system won't suck any in.
If the clutch needs to engage to draw in refrigerant but the clutch won't engage without enough refrigerant is a big old catch 22. Do I get around that by jumpering the pressure switch to engage the clutch?
Submitted: 6 months ago.Category: Pontiac
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Answered in 3 minutes by:
8/5/2017
Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago
Gary
Gary, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 1,489
Experience: Senior Technician
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Hello! My name is Gary.
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I'm reviewing your question now, and will post back with a reply shortly.

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Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

Hi Matthew,

Are you pulling vacuum, and then charging?

It won't take the full charge if there isn't a vacuum to start with.

Gary

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Customer reply replied 6 months ago
Pulling down a -30 vacuum for 45 minutes using a JB Industries 2 cycle 6cfm pump
Customer reply replied 6 months ago
Pulling a -30 vacuum for over 30 minutes.
Customer reply replied 6 months ago
Using a JB Industries 2 cycle vacuum pump. All equipment is top of the line. No auto part store garbage.
Customer reply replied 6 months ago
Pulling vacuum with H and L open. Close H and L. Turn off vacuum pump. Holding at -30. Disconnect yellow from pump to refrigerant. Open refrigerant. Purge the line. Start car. Turn on AC. Open L on manifold. And nothing. It won't take a charge.
Customer reply replied 6 months ago
Hook up high and low sides. Close both high and low. Turn on vacuum pump. Open high and low. Vacuums down to -30 for half an hour. Close high and low. Turn off vacuum pump. Unhook yellow from vacuum and hook it up to refrigerant. Open refrigerant. Purge the line. Turn on car. Turn on AC. Open low side. And - NOTHING!
Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

Can you charge it on the high side before starting the engine?

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Customer reply replied 6 months ago
Nope.
Customer reply replied 6 months ago
Nope. I tried.
Customer reply replied 6 months ago
If the clutch must engage to draw in refrigerant - but the clutch won't kick on until it has enough refrigerant, that means you will never be able to charge it.
Customer reply replied 6 months ago
If I jumper the pressure switch to force the clutch to engage, will that then draw in the charge?
Customer reply replied 6 months ago
Also, the system will hold vacuum at -30 for an hour long sit and check. But, it won't hold it overnight. Is that normal not to hold it that long? Or does that mean I have a small 24 hour leak?
Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

Did you flush the whole system after the compressor failure, and replace the filter?

You shouldn't charge any system from empty on the low side these days.

You must have a blockage if it won't take the charge on the high side.

I wouldn't worry about not holding vacuum over 24 hours, could be part of your charging station.

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Customer reply replied 6 months ago
If I vacuum down to -30 and come back in an hour, it will still be holding at -30. But, if I let it sit overnight, it loses the vacuum back up to 0. Is that normal? Probably leaking from the quick connects on the ports? Or does that mean I have a small 24 hour leak?
Customer reply replied 6 months ago
I replaced the compressor, orriface tube and accumulator. Put 4 ounces of PAG 46 in the compressor and 4 ounces in the accumulator. I did not flush it because it was just flushed 200 miles ago when the first compressor was installed.
Customer reply replied 6 months ago
Can I charge it on the low side if I jumper the pressure switch to engage the clutch? Or will that fry the compressor?
Customer reply replied 6 months ago
I correct that you charge on the low side with the engine and air running or the high side with the engine off. But never on the high side with the engine and AC running?
Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

If it is still holding -30 after 1 hour, I'd say put the gas in.

Every car I do, I pull vacuum, short wait, then charge via the high side with the specified weight of R134a.

You can suck it on the low side, if you jumper the pressure switch, engine running.

Charging via the high side is engine off only.

Gary

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Customer reply replied 6 months ago
Got it. If I jumper the pressure switch to engage the clutch, will I fry the clutch or compressor? Or is it safe for a few minutes?
Customer reply replied 6 months ago
Do the auto part store 12 ounce cans of R134a have enough push and pressure to charge on the high side through the AC manifold? I guess I'll try high side engine off first. Then I'll try low side engine on and jumper the clutch.
Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

The vacuum generated while evacuating should draw in sufficient on the high side, engine off.

If you need to, you can then suck in on the low side, engine running.

The average systems I deal with take about 25 ounces, 700 grams.

Gary

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Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

Hi Matthew,

I hope this had made sense for you.

All the best.

Kind regards

Gary

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Pontiac Mechanic: Gary, ASE Certified Technician replied 6 months ago

Hello again,

Do you need any further help?

I hope my advice has been of assistance to you.

Kind regards

Gary

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Gary
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