A/C charging questions
Thread Starter
Le Mans Master
Joined: Apr 2005
Posts: 6,366
Likes: 432
From: Seattle Area WA
A/C charging questions
I'm getting close to getting the '76 on the road for summer and I just finished installing the A/C components (A6 and VIR). Question is, Auto Zone loans out Vacuum pumps rated at 2.5cfm, will a 2.5cfm pump pull down the OEM system enough to fill with R-12? From what I understand, a 2.5 cfm pump is pretty small, might take awhile to pull the system down right?
Thanks for the help/
Thanks for the help/
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
It'll be fine. Run it for a couple of hours to make sure any moisture in the sytem gets boiled out. Close both the valves, let it set and watch the gauges for any movement that could indicate a possible leak. Add oil if needed and charge it (low side) with the correct weight/amount of R-12.
Melting Slicks
Joined: May 2011
Posts: 2,753
Likes: 119
From: Springfield Missouri
There should be a sight glass on the high side, when charging, you should see small bubbles flowing until it is full of freon. You will have to jump the low pressure switch to get the compressor to kick in until it has enough freon to satisfy the switch. But you must know all of this since you are charging the car with a controlled substance( r-12).
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
as Tim said,
the 2.5 cf pump will work just fine
Leave it on for a few hours and close it in for atleast 30 minutes to see if the vacuum level falls (leak check).
Neal
the 2.5 cf pump will work just fine
Leave it on for a few hours and close it in for atleast 30 minutes to see if the vacuum level falls (leak check).
Neal
Thread Starter
Le Mans Master
Joined: Apr 2005
Posts: 6,366
Likes: 432
From: Seattle Area WA
Thanks guys. No I have not read where I need to bypass the pressure switch to turn on the compressor at a certain time. When are you suggesting that be performed?
Last edited by Scott Marzahl; May 9, 2012 at 11:17 AM.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
If you have the system properly evacuated, then charge it without the engine running. You should be able to get more than enough refrigerant in to set the pressure switch. Then run the engine and finish charging.
Le Mans Master
Joined: Jun 2007
Posts: 7,666
Likes: 1
From: Where it's always hot as Hell-South Louisiana.
St. Jude Donor '07-'08-'09-'10-'11-'12-'13
What noonie says.
To charge a system near completion with the engine off & compressor not running: Check the system capacity (usually stamped near the evap coil under the hood) . If it says 3 pounds, X ounces... you can charge that amount thru the high side as a liquid from the new canister of refrigerant.,assuming that a prpoer vacuum has been pulled on the system prior. Just make sure you allow the system to sit for some time before cranking , to allow the liquid to flash off at ambient temps. This procedure is ususally done by an experienced tech, so be careful that you are certain the correct quantity is installed and not to overcharge.This should take care of the low pressure switch from holding the system out to complete the charge once the motor is running.
Confused ?
Hope not.
Thread Starter
Le Mans Master
Joined: Apr 2005
Posts: 6,366
Likes: 432
From: Seattle Area WA
Thanks for all the advice and verifying that I didn't need to bypass the pressue switch. What should a tight system pull down to? Just trying to get my ducks in a row before I perform this task in a week or so, still waiting on the Robinair gauge/hose set to arrive.
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Race Director
Joined: Sep 2001
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From: Wellington, FL
St. Jude Donor '11 thru '25
Just so you know Scott, which you probably already do, a pound of refrigerant is 16 ounces which used to be the amount contained in refrigerant cans back in the '60's. This carryovers to today as some still think that cans contain a pound of refrigerant. Most cans now contain 12 or 14 ounces so remember to adjust for this. A car requiring 3 pounds or 48 ounces would require 4 12 ounce cans.
As for vacuuming the system, a good pump should quickly take the system down under 29 in. HG at sea level.
As for vacuuming the system, a good pump should quickly take the system down under 29 in. HG at sea level.
Last edited by Jud Chapin; May 9, 2012 at 04:12 PM.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Jumpering the low pressure switch is a trick when you're working flat rate and need to crank as much thru your shop/work area as possible every day. Anything to make whatever a little faster- be it removing the snap ring from your impact and collapsing it so it's easier to get sockets on and off or anything else you can think of.
noonie got it again- the system should take enough to keep the low pressure switch from cycling on and off so you can top the system with the final amount by weight.
noonie got it again- the system should take enough to keep the low pressure switch from cycling on and off so you can top the system with the final amount by weight.
