Trying to charge A/C system...
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Joined: Dec 2024
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From: Alexandria VA
Trying to charge A/C system...
I'm hoping someone will watch this video and give me something to check that I haven't yet... While trying to charge the system after total overhaul (new compressor, condenser, dryer, orifice tube etc...), the compressor cycles on and off with the resulting pressures. Compressor engages, low side pressures rapidly rise to a safety cut off, and the high side pressure drops. Compressor turns off, pressures immediately begin to level off, compressor engages and so on and so on. I am able to push compressed air through the system, I do not think it's clogged. I applied vacuum to the system for 6 hours and it held as it should. I will talk to a local shop about taking it in. Thank y'all.
https://youtube.com/shorts/9IfjGe19oUU?si=1G8Lsd64HtG4nheF
https://youtube.com/shorts/9IfjGe19oUU?si=1G8Lsd64HtG4nheF
Thread Starter
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From: Alexandria VA
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I'm hoping someone will watch this video and give me something to check that I haven't yet... While trying to charge the system after total overhaul (new compressor, condenser, dryer, orifice tube etc...), the compressor cycles on and off with the resulting pressures. Compressor engages, low side pressures rapidly rise to a safety cut off, and the high side pressure drops. Compressor turns off, pressures immediately begin to level off, compressor engages and so on and so on. I am able to push compressed air through the system, I do not think it's clogged. I applied vacuum to the system for 6 hours and it held as it should. I will talk to a local shop about taking it in. Thank y'all.
https://youtube.com/shorts/9IfjGe19o...8Lsd64HtG4nheF
https://youtube.com/shorts/9IfjGe19o...8Lsd64HtG4nheF
The compressor cycling would then be due to the high side pressure transducer shutting off the compressor due to low pressure. I think it shuts off somewhere in the 40psi range.
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From: Alexandria VA
I am seeing flow in the sight glass of your gage set so my thought is you have the gage set valves open. If so, this directly connects the high side to the low side of the system through your gage set. To read system pressures, those valves should be closed.
The compressor cycling would then be due to the high side pressure transducer shutting off the compressor due to low pressure. I think it shuts off somewhere in the 40psi range.
The compressor cycling would then be due to the high side pressure transducer shutting off the compressor due to low pressure. I think it shuts off somewhere in the 40psi range.
Are those pressure fluctuations normal while charging the system? I don't want to jump the compressor on if the pressures are wrong....
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From: Alexandria VA
Thread Starter
Instructor
Joined: Dec 2024
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From: Alexandria VA
I spoke with a local shop, he said something that I have wondered: sometimes the little 12oz cans of freon don't have enough oomph to charge. He suggested it may just need their machine to do the charging. I am leaning that way too, because I just can't figure it out! I will continue to monitor this thread and take any advice before I get a chance to bring it in to a shop.
Drifting
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From: Long Island New York
I didn’t have your issue when I did mine.
after doing a proper oil balance, I did have to cheat the compressor to get her going, and all worked all well using my gauges and weighing Freon cans on a scale.
some charge their system with engine off on the high side, (engine off!)
You will have to read more on that to understand what your doing.
I did not go that route.
after doing a proper oil balance, I did have to cheat the compressor to get her going, and all worked all well using my gauges and weighing Freon cans on a scale.
some charge their system with engine off on the high side, (engine off!)
You will have to read more on that to understand what your doing.
I did not go that route.
Instructor
Joined: Apr 2019
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From: South Texas, US Army-Retired
Hey 11B. Several years ago, I did a Fiero system, just like you are doing now. It was such a PITA to get it correct. The can system is difficult getting the freon amounts (weights) correct, I swear I'll never do it again. If there is a next time, I'll get the shop with their fancy machine to do it. Good luck with your project.
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From: Alexandria VA
I didn’t have your issue when I did mine.
after doing a proper oil balance, I did have to cheat the compressor to get her going, and all worked all well using my gauges and weighing Freon cans on a scale.
some charge their system with engine off on the high side, (engine off!)
You will have to read more on that to understand what your doing.
I did not go that route.
after doing a proper oil balance, I did have to cheat the compressor to get her going, and all worked all well using my gauges and weighing Freon cans on a scale.
some charge their system with engine off on the high side, (engine off!)
You will have to read more on that to understand what your doing.
I did not go that route.
Last edited by Eleven Bravo; Jun 30, 2025 at 03:52 PM.
Thread Starter
Instructor
Joined: Dec 2024
Posts: 125
Likes: 73
From: Alexandria VA
Hey 11B. Several years ago, I did a Fiero system, just like you are doing now. It was such a PITA to get it correct. The can system is difficult getting the freon amounts (weights) correct, I swear I'll never do it again. If there is a next time, I'll get the shop with their fancy machine to do it. Good luck with your project.
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Instructor
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Posts: 125
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From: Alexandria VA
When the compressor turns on, the low side pressure rises rapidly and the high side pressure drops. When it turns off, they rapidly begin to level out, low side drops, high side rises. The compressor is only staying on for a second before shutting off. In the video, low side is on the left