Vacuming Dual Front Rear AC Sytem.
- Thread starter DougA
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I don't think there is anything special. I've done mine several times 2005 Yukon Denali. It takes a minute or two to reach maximum vacuum because of the larger capacity. I usually vacuum for about an hour. You may also want to consider replacing the receiver/dryer and orifice tube if you haven't already.
SnowDrifter
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Nope. Systems are plumbed in parallel with the rear circuit on a thermostatic orifice that operates passively.
Yes on the accumulator and orifice(s) and when you get to the max vacuum, which always depends on the elevation above or below sea level, let it stay on vacuum for about 15 minutes and then shut off the vacuum pump and watch the gauge. If the vacuum reading changes within 10 minutes by a noticeable level, you have a leak. If it moves an inch or two, you are ok to charge the system.
SnowDrifter
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I'll take this a step further and volunteer how I do mine
Vacuum system for 10min
Close off the vacuum valve, mark gauges, let it sit for 45 mins. It's enough time generally for even the smallest leak to be noticed - barring some strange o-ring issues that seal under vacuum but leak under pressure.
ANY movement is a fail for me. In inch or two in 10 minutes will lose the entirety of your vacuum in an hour and a half. Not something I would be able to call sealed.
After that, I'll move to the drying pull, which is flipping the pump back on and letting it go for another length of time. A shop will typically do it for 15 minutes. I do mine for 45 to an hour. It's just enough time to grill something and have a beer or 6.
The longer here, the better. The desiccants are rather reluctant to let go of any stored water.
After that, THEN I charge. And go by weight. Physically measure how heavy your cans are before and after you fill.
Oh, and don't forget to purge the air from your gauge / fill lines
I always gave up an inch or two because the gauges themselves could have a problem. Whatever works for anyone is always the best.
To some that don't know, the moisture pulled out of the desiccant is caused by the moisture boiling in a vacuum and turns to a gas/air and the pump pulls that out. That is what I was taught gobs of years ago. If the desiccants have changed over the years I am not aware. Any moisture laying in the system will boil at vacuum and be pulled out.
I actually saw a shop once in the Death Valley area and they were below sea level and the vacuum pump pulled more than 30 inches of vacuum. That amazed me.
To some that don't know, the moisture pulled out of the desiccant is caused by the moisture boiling in a vacuum and turns to a gas/air and the pump pulls that out. That is what I was taught gobs of years ago. If the desiccants have changed over the years I am not aware. Any moisture laying in the system will boil at vacuum and be pulled out.
I actually saw a shop once in the Death Valley area and they were below sea level and the vacuum pump pulled more than 30 inches of vacuum. That amazed me.
SnowDrifter
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The way I see it, if the gauge has an issue, it should be scrapped. It is the nature of refrigerant systems that you must be able to trust your equipment.
A moving gauge. Is that a leak in the system? Or a leak in my equipment?
Hmm it works fine for 5 minutes then stops. Is the orifice clogged? Or did my gauge introduce air and moisture to the system?
It works but the evaporator keeps freezing up. Is my refrigerant too low? Or did the gauge leak some out and mess with my measurements?
etc etc.... If your gauges are shot, just recycle the things and move on
A moving gauge. Is that a leak in the system? Or a leak in my equipment?
Hmm it works fine for 5 minutes then stops. Is the orifice clogged? Or did my gauge introduce air and moisture to the system?
It works but the evaporator keeps freezing up. Is my refrigerant too low? Or did the gauge leak some out and mess with my measurements?
etc etc.... If your gauges are shot, just recycle the things and move on
I agree with you completely. I always trusted my gauges but in some of the shops I ran the a/c machine had suspect gauges. I had my set of tools at home when I ran shops. As a tech I always used my own gauges.
