AC question: pull vacuum on service hoses before connecting?
- Thread starter tiredguy
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I've only purged the air out of hoses with refrigerant for years. Just a small shot. Its a deminimus release.
The simple answer is NO!
So your suggesting pulling a vacuum on the whole gauge set before connecting? I suspect most of that vacuum would escape on connecting - don't know. No expert for sure but I never have. I do purge the yellow hose if I am filling.
Why not partially fill the system with some refrigerant first to circulate it through the system and maybe bleed some of that off at the service ports? Then pull a vacuum on what's left. After that purge the fill line to the gauges after connecting the refrigerant can.
I have vacuumed residual refrigerant before, nothing bad happened. I believe the shop a/c machines also vacuum out refrigerant as well for recovery purposes.
I have vacuumed residual refrigerant before, nothing bad happened. I believe the shop a/c machines also vacuum out refrigerant as well for recovery purposes.
Well your first mistake was listening to Scotty let alone watching his sewage.
Professionals in the HVAC industry purge with nitrogen afaik. I think most mechanics purge with refrigerant if they are not using those automated machines.
Professionals in the HVAC industry purge with nitrogen afaik. I think most mechanics purge with refrigerant if they are not using those automated machines.
Owen Lucas
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I've never heard of this. Maybe if you are working on very sensitive and specialized deep-freeze units with uncommon refrigerants that are prone to contamination, like lab equipment. But for automotive/residential/commercial use. I don't think it will make a difference. What are you vacuuming out?
CleanSump
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If you're talking about filling then either purge with the correct refrigerant or pull a vacuum. If just pulling a vacuum, then what's the point? You're pulling a vacuum and nothing is going in.
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I've always just hooked all three hoses up, opened both manifold valves and let it evacuate for a couple of hours. Then I'll close the manifold valves, shut off the pump then monitor the low side gauge for awhile to check for a loss of vacuum. If then needle holds then there shouldn't be any significant leaks.
Here's the tricky part, hooking up the first refrigerant can. Obviously disconnecting the line at the vacuum pump introduces ambient air into that hose. Probably not a big deal in the desert Southwest but I live in coastal South Texas, where we have air you can wear. All I do is attach the hose to the service adapter on the can, crack the hose loose where it attaches to the manifold then invert the can and open the valve on the adapter until the refrigerant just starts to flow. Once visible gas starts leaking from the loosened hose fitting, I just tighten it back up. This purges the air from that hose and I'm now ready to start the engine and begin servicing.
It might seem a bit excessive, but the more humid air you keep out of the system the better.
Here's the tricky part, hooking up the first refrigerant can. Obviously disconnecting the line at the vacuum pump introduces ambient air into that hose. Probably not a big deal in the desert Southwest but I live in coastal South Texas, where we have air you can wear. All I do is attach the hose to the service adapter on the can, crack the hose loose where it attaches to the manifold then invert the can and open the valve on the adapter until the refrigerant just starts to flow. Once visible gas starts leaking from the loosened hose fitting, I just tighten it back up. This purges the air from that hose and I'm now ready to start the engine and begin servicing.
It might seem a bit excessive, but the more humid air you keep out of the system the better.
I think what the OP is trying to do is diagnostics of a currently full system. A full evac / refill obviosly doesn't matter, your going to pull a long vacuum, purge the yellow line and fully refill.
Still, I doubt the red and blue hoses hold enough air to do much, and there at atmospheric pressure. The issue is during diagnostic there going to fill with refrigerant and when your done whatever amount that was will now no longer be in the system. In fact thinking out loud, if you pull a vacuum its going to lose even more refrigerant because there is nothing else in the two hoses.
I don't. Once I'm done vacuuming the system down, I close the valves on the manifold and then the vacuum pump. When I hook the yellow hose to the gauges from the refrigerant tank, I push the Shrader valve down on the gauges for the yellow line until a small shot of refrigerant comes out which purges the yellow line of air. I then open the low side and let the vacuum pull in the refrigerant and then eventually start the vehicle until the programmed amount on my scale beeps and I shut the valve closed on my low side gauge and then the valve on the refrigerant tank.
I am the original poster of this thread.
The AC compressor in my car doesn't turn on. I am trying to figure out if it is not turning on due the low pressure or something else.
I thought I had a leak and had no pressure. I just borrowed a set of gauges my my neighbor. I Just connected them with the car off and or running it reads the same (ac won't turn on). Outside temp is 56F and the static reading is about 38. Should the compressor turn on with the pressure at 38? If so , I guess the issue is not due to a leak or low pressure.
The vehicle is a 2006 VW Jetta, the compressor doesn't have a clutch it has an ac compressor control valve.
Any info you can share will be helpful.
Thanks
The AC compressor in my car doesn't turn on. I am trying to figure out if it is not turning on due the low pressure or something else.
I thought I had a leak and had no pressure. I just borrowed a set of gauges my my neighbor. I Just connected them with the car off and or running it reads the same (ac won't turn on). Outside temp is 56F and the static reading is about 38. Should the compressor turn on with the pressure at 38? If so , I guess the issue is not due to a leak or low pressure.
The vehicle is a 2006 VW Jetta, the compressor doesn't have a clutch it has an ac compressor control valve.
Any info you can share will be helpful.
Thanks
Most A/C pressure cut off switches interrupt power to protect the compressor when the low side (suction) pressure drops below 25 psi. Therefore, your compressor should be energizing based upon the 38 psi shown in your photo in Post #14. Your Jetta uses a G65 transducer to send the signal instead of simple electrical contact switches. The sensor is inexpensive and can be easily changed out without evacuating the refrigerant. You can try to electrically diagnose the G65 sensor, but it may not be worth the effort compared to simply replacing it.
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thanks, I believe the 2.5L gas model only has a control valve and not a high pressure valve. I could be wrong, I am new at this and tring to understand the system
I stand corrected, my vehicle does have the high pressure valve switch. I was confused as I thought it was mounted to the compressor it is not, it is mounted down low near the radiator fans.
Thanks again for posting. I have been doing lots of research into the ac system and is seems like high pressure switch in the video you posted turns off the system when the pressure gets too high. Both of my fans turn on when I turn the ac on. I believe if the high pressure switch was bad and cutting off the ac then the fans wouldn't work.
Still trying to figure out what is going on.
Thanks again.
If your outside temps were 56 degrees, your static pressure should be close to that so you are probably low on refrigerant. Are you saying that the gauges read the same whether the car is running with the AC on and when it's turned off?
Whether or not the AC would turn on with those pressures would be dependent on what service information says for that vehicle. The only way to really know if your system is operating normally is to fill the system up by the manufacturer's weight and see how the AC performs. If the compressor still does not come on, you may have an electrical problem. You really need a good wiring diagram to see what all is in the system electrically if that is the case so you can break the electrical system down and test each section.
I just hooked gauges up to the system and get a reading of 38 psi on both gauges showing it is equalized. Note - It was about 56F outside. According to the F R134a blue scale on the gauge 38 psi corresponds to about 44 F. When I made this measurement it was about 56 outside.
The compressor shuts off when the is refrigerant pressure too low (< 2.0 bar). 2 bar = 19 psi. So at 38 pis I am above that. So I guess this is not what is keeping the compressor from running.
