? for AC experts......
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,354
Likes: 214
From: Beecher Illinois
? for AC experts......
regarding evacuation and holding vacuum.
Pulled 30 in of vacuum, ran the pump for 60 minutes.
The pamphlet that came with my gauges(professional set bought 20 years ago)says after the pump is removed vac should hold for just a minute and "any rapid loss of vac is a serious leak".
GM shop manual says 5 minutes. Seems to hold for that long OK.
How about an hour? Or 2 or 3? Any loss expected?
Seems theoretically it should hold vac forever if no leaks, but realistic?
Harder to hold vac than pressure?
I'm doing just a basic evac and charge for a friend's low mile original car. System was completely empty, untouched for probably the life of the car. Compressor when jumped made some noise. I did add some oil directly into the compressor and replace the 2 O rings on the back of it. It did quiet down.
Don't plan on tearing anything else down.
If it was mine I'd go ahead and add the R12 and see how long it lasts, but don't want to charge someone else $60 for freon that may not last at least all summer.
Pulled 30 in of vacuum, ran the pump for 60 minutes.
The pamphlet that came with my gauges(professional set bought 20 years ago)says after the pump is removed vac should hold for just a minute and "any rapid loss of vac is a serious leak".
GM shop manual says 5 minutes. Seems to hold for that long OK.
How about an hour? Or 2 or 3? Any loss expected?
Seems theoretically it should hold vac forever if no leaks, but realistic?
Harder to hold vac than pressure?
I'm doing just a basic evac and charge for a friend's low mile original car. System was completely empty, untouched for probably the life of the car. Compressor when jumped made some noise. I did add some oil directly into the compressor and replace the 2 O rings on the back of it. It did quiet down.
Don't plan on tearing anything else down.
If it was mine I'd go ahead and add the R12 and see how long it lasts, but don't want to charge someone else $60 for freon that may not last at least all summer.
Last edited by KapsSA; Jul 2, 2012 at 11:18 PM.
Limping across the line
Joined: Oct 2002
Posts: 5,295
Likes: 109
From: Peoria Az
It should be a air tight system no vac or pressure loss.
But compressor front seals are known to go bad. Look for oil stains from front of compressor pulley.
A good idea is after sucking down the systm and holding vacuum for a awhile, is to charge the system with 150psi of dry air. Then see if it holds for a couple of hours.
My 442 had a leak in the condenser that was only present under pressure
But compressor front seals are known to go bad. Look for oil stains from front of compressor pulley.
A good idea is after sucking down the systm and holding vacuum for a awhile, is to charge the system with 150psi of dry air. Then see if it holds for a couple of hours.
My 442 had a leak in the condenser that was only present under pressure
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 27
From: Florida
Depends on a few factors.
How good the pump is and how much moisture it will remove, basically, how close to a perfect vacuum it can get.
How good the hoses on your gauge set are.
I test them for about 15 min and make sure it doesn't drop more than point is normal. On a residential sealed unit, it will hold for hours or days, on a mobile system, it won't.
I would run the pump for a couple hours and inject dye with the refrigerant. There was obviously a leak, but since you don't know the real history, there is no way to tell anything more.
Unless he wants to replace all hoses and seals etc, you can't guaranty against leaks.
How good the pump is and how much moisture it will remove, basically, how close to a perfect vacuum it can get.
How good the hoses on your gauge set are.
I test them for about 15 min and make sure it doesn't drop more than point is normal. On a residential sealed unit, it will hold for hours or days, on a mobile system, it won't.
I would run the pump for a couple hours and inject dye with the refrigerant. There was obviously a leak, but since you don't know the real history, there is no way to tell anything more.
Unless he wants to replace all hoses and seals etc, you can't guaranty against leaks.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Holding vacuum for just a few minutes or so is not enough time to determine if there are SMALL leaks. An hour or more is more like it but shops can't afford to put that much time into a job. And besides, when those directions were written, refrigerant was $1.00 a can or so.
I have at times let mine sit overnight to be fairly sure it's leak free. If you have the time, let the gauges sit for at least an hour IMO. Better to be sure then to have to evacuate the system again. If you have an electronic leak detector, you can go over the system again checking for leaks after adding just the first can.
I have at times let mine sit overnight to be fairly sure it's leak free. If you have the time, let the gauges sit for at least an hour IMO. Better to be sure then to have to evacuate the system again. If you have an electronic leak detector, you can go over the system again checking for leaks after adding just the first can.
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,354
Likes: 214
From: Beecher Illinois
No oil on the hood from the front seal, no noticeable oil on the bottom of the compressor from bad case O rings. Who knows if either will start leaking when pressurized, tho?
After an hour I was down to 26 in of vac, 5 hours and the vac was pretty much gone.
Don't know how good my gauge hose seals are, they are kinda chewed up.
I'll have to give him a call tomorrow and see if he wants to give it a try.
I know I myself have no problem adding a can of R22 to my home system every year or topping off one of the Vettes if needed.
After an hour I was down to 26 in of vac, 5 hours and the vac was pretty much gone.
Don't know how good my gauge hose seals are, they are kinda chewed up.
I'll have to give him a call tomorrow and see if he wants to give it a try.
I know I myself have no problem adding a can of R22 to my home system every year or topping off one of the Vettes if needed.
Last edited by KapsSA; Jul 3, 2012 at 12:15 AM.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
If you're serious about doing HVAC work, pulling deep vacuums, you're needing to get hold of a micron gauge, as will show a leak right away. Strange thing, if a new compressors seal is leaking from the factory, your'e really needing to lube it with oil. Usually this is done by running the system fully charged with refrigerant and oil, so could be tough at first. This could turn out to be a rather long discussion, but good idea putting in a UV dye shot, as much easier to leak trace later on.
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,354
Likes: 214
From: Beecher Illinois
There ya go!!I've been fighting with the hose end seals for years. They tend to get chewed up pretty fast. I've been making new seals out of pieces of vacuum line and for the most part no problems.
Vac'd it down one more time after messing with my hose seals again. Lost vac REAL quick this time.
Eliminated the high pressure hose, just using ONE hose, the low pressure side.
Held vac steady for 30 minutes
The end seal on the high hose didn't look bad but must have been.
Charged it with just the low line hose hooked up, then attached the high line hose to check my readings.
Good numbers, ICE cold air.
I probably should try to locate CORRECT hose end seals for my gauges now............
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Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 27
From: Florida
There ya go!!I've been fighting with the hose end seals for years. They tend to get chewed up pretty fast. I've been making new seals out of pieces of vacuum line and for the most part no problems.
Vac'd it down one more time after messing with my hose seals again. Lost vac REAL quick this time.
Eliminated the high pressure hose, just using ONE hose, the low pressure side.
Held vac steady for 30 minutes
The end seal on the high hose didn't look bad but must have been.
Charged it with just the low line hose hooked up, then attached the high line hose to check my readings.
Good numbers, ICE cold air.
I probably should try to locate CORRECT hose end seals for my gauges now............
Go to your local commercial/residential a/c distributor, they will have just the seals.
I know it's tempting, but don't tighten them so tight. Light finger pressure is more than enough. Mine are probably 15 years old.