New Parts But Can't Pull a Good Vacuum

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Esox
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New Parts But Can't Pull a Good Vacuum

Post by Esox »

I have a 2000 Chevy Silverado 5.3L with single A/C. I have had a slow leak for a couple years. It appeared to be the condenser based on a UV light inspection and the dye in the oil. I bought a set of gauges and a vacuum pump from Harbor Freight. I then purchased a new condenser, accumulator, and both the lines that go into and out of the condenser (just to be safe). I assembled it all together and ensured that each fitting had an o-ring/gasket thing with a small amount of PAG 45 oil applied. I hooked up the vacuum pump and all I can get is -5 in Hg. It will drop down to -15 in Hg if I close the high pressure side and just suck on the low pressure line. I unhooked the condenser, started the pump, and physically plugged both the inlet and outlet lines with my finger. I feel suction on the bottom line (outlet) but do not feel any suction on the top line (from compressor).

When I leave everything as-is and just turn the switch off to the pump, it jump back to zero right away. I think this means I am not holding the little bit of vacuum that I have, correct?

Any ideas on what could be wrong or how to troubleshoot? I am a total newbie, so my apologies in advance.

THANK YOU!
Esox
tbirdtbird
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Re: New Parts But Can't Pull a Good Vacuum

Post by tbirdtbird »

1. Is your vacuum pump powered by an electric motor?
2. Connect up your gauge set so that it is the only thing connected to the vac pump. ie don't connect the red and blue hoses to the car, and see what kind of a vacuum you can get. It sounds like there are leaks
3. report back
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Esox
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Re: New Parts But Can't Pull a Good Vacuum

Post by Esox »

1. Is your vacuum pump powered by an electric motor?
Yes.

2. Connect up your gauge set so that it is the only thing connected to the vac pump. ie don't connect the red and blue hoses to the car, and see what kind of a vacuum you can get. It sounds like there are leaks
No leaks.

3. report back
Since I now knew that the pump was working fine, I decided to try to trace the leak in the system. I used compressed air to blow into the yellow gauge line. Sure enough, I heard an air leak by the new accumulator where it attaches to the evaporator. It turns out that I did not align the port properly and when I tightened down the nut on the firewall stud it just jammed it in and did not create a seal. I removed it, but that accumulator port is now damaged. I quickly ran to an auto parts store and purchased a new accumulator. I will try to install it tonight and hope that I did not create a new leak at the evaporator junction. I will report back with an update.

On a side note, I drained about a 1/4 cup of PAG oil out of the old condenser, so I plan to recharge that amount of oil back into the system. My internet searches suggest adding 2 oz. of additional oil to the accumulator if it is replaced. Does this seem reasonable or should I just add 1 oz.? I have heard claims that it is better to have not enough oil versus too much.

Thanks,
Esox
tbirdtbird
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Re: New Parts But Can't Pull a Good Vacuum

Post by tbirdtbird »

Drill a hole in the bottom of old accum and measure what comes out. Put that amount back in the new
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JohnHere
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Re: New Parts But Can't Pull a Good Vacuum

Post by JohnHere »

One-quarter cup equals approximately 2 fluid ounces. So, yes, put 2 fluid ounces of the proper weight PAG oil back into the condenser.That's the amount I was going to suggest anyway.
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Esox
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Re: New Parts But Can't Pull a Good Vacuum

Post by Esox »

UPDATE: I put just a tiny bit over 2oz of PAG46 oil with dye into the replacement accumulator, installed it, and pulled a vacuum for 2 hours. I then closed the gauges and it held the vacuum reading for one hour without moving at all. I then proceeded to start charging the R134a. The first can went VERY slow. I was concerned, but shaking the can and patience finally paid off. The second can went pretty fast. The third can I used a digital kitchen scale to weigh to have a final charge of 32oz R134a. The truck now blows nice cold air!

I think I am good now. :)

Lesson learned is to be patient installing things. I should have been more diligent aligning the accumulator port. This was my very first a/c job. I feel a little bit more confident now.

Thanks!
Esox
tbirdtbird
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Re: New Parts But Can't Pull a Good Vacuum

Post by tbirdtbird »

Glad you got it squared away, that is why we are here! And patience is never a bad thing, especially with something you have never done before.
Having hot water in a small tub and partially submerging the small 134 cans can speed up the charging method you are using (vapor charging).
Good luck.
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Cusser
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Re: New Parts But Can't Pull a Good Vacuum

Post by Cusser »

Esox wrote: Fri Sep 23, 2022 4:09 pm Lesson learned is to be patient installing things. I should have been more diligent aligning the accumulator port.
Esox - I can't say for sure on a 2000, but I remember our 1994 Suburban having very troublesome, poorly-engineered connection at the accumulator. And I saw lots of posts on accumulator or evaporator threads stripping or galling. By at least 2005 (we had a 2005 Yukon) this had been re-engineered to a much better situation.
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JohnHere
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Re: New Parts But Can't Pull a Good Vacuum

Post by JohnHere »

OP, be aware that those small cans of refrigerant might contain fewer than 12 ounces. The only way to know for sure is to weigh-in each can (or partial can) to arrive at the total amount for your system.
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Esox
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Re: New Parts But Can't Pull a Good Vacuum

Post by Esox »

Yes, the design of where the evaporator and accumulator meet is not great. I proved that!

Good point on the 12 oz. cans. I'll measure each one next time I do a job like this. My final numbers were 38 low and 190 high. It was fairly cool outside air temperature.
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