AC guages
Thread Starter
Team Owner
Joined: Oct 2004
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From: Bergen County, NJ Democrats, doing for the country what they did for Michigan
AC guages
OK, I got a set of R12 AC guages. I want to check the pressure in my AC since I just filled it and have no idea what''s in there.
The compressor clutch was cycling every few seconds so it needed a charge. I filled it until the clutch stayed on and dumped the rest of the can in there.
There is no rattling from the compressor that would indicate an over charge, but I want to make sure.
So...to the piont...how are these things use? There's two gauges and three hoses, red, yellow, blue.
I don't want to add any more freon, just check what I have. No, they are not new, and no they didn't come with instructions. They have been hanging in my dad's garage for years.
Thanks.
The compressor clutch was cycling every few seconds so it needed a charge. I filled it until the clutch stayed on and dumped the rest of the can in there.
There is no rattling from the compressor that would indicate an over charge, but I want to make sure.
So...to the piont...how are these things use? There's two gauges and three hoses, red, yellow, blue.
I don't want to add any more freon, just check what I have. No, they are not new, and no they didn't come with instructions. They have been hanging in my dad's garage for years.
Thanks.
Last edited by jsup; May 7, 2008 at 07:28 AM.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Red is the high side - you'll need an adaptor for GM. Blue is Low. Make sure the gage valves are closed. Prop the throttle so that it's running at 1200 to 1500 rpms. Disconnect the fan switch on the High Line so that the Main Fan is running. Put the system on Max and leave the windows down. A good high side shouldn't exceed 2.2 to 2.5 times the air temp across the condensor which can be 10 degrees higher than ambient on a bottom feeder - particularly if you in a garage. Low is going to vary with outside air temp, but 28 to 32 is typical. Do check the Low Pressure switch cutoff by pulling the blower connector. Observe the Low gage and note the pressure the compressor cuts out at - should be 25 psi for R12. Check operation of the fan switch by plugging it back in. High side should rise to 228 and the fan should kick on. Pressure should drop to about 190 psi and the fan should kick off (note if it's 80 degrees or better, it might not get that low). Post your pressures, center vent temp and outside air temp or use the Charts in your Service Manual.
Thread Starter
Team Owner
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From: Bergen County, NJ Democrats, doing for the country what they did for Michigan
Melting Slicks
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From: Austin Texas
Last edited by MikeC4; May 7, 2008 at 04:46 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Never seen a separate valve on a manifold gage set for the charge hose. You open the low side valve when you charge. The only time you'd open the high (and the low) is while pulling a vacuum. In all other situations, both valves - on the gage set - remain closed.
Thread Starter
Team Owner
Joined: Oct 2004
Posts: 35,065
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From: Bergen County, NJ Democrats, doing for the country what they did for Michigan
That answered my question. The valves are between the freon source (yellow hose) and the high/low side. Red/blue hose.
Cool.
I'll figure out what I need.
Can I just measure the low side and get close?
Cool.
I'll figure out what I need.
Can I just measure the low side and get close?
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
You could, but I'd measure both sides. Design is to maintain average head pressures of 200 psi (between about 70 and 90 degree ambients) and the low will fall into place. Now if you live where summer temps routinely exceed 100, you might pay particular attention to low; ie, aim for a slight undercharge - say no more than 35 psi on the low if the outside air is 100. This may make it a few degrees better at the vents (high 50's instead of low 60's) but it's going to cycle a lot more when it's below 70 which leads to more wear and tear.
Thread Starter
Team Owner
Joined: Oct 2004
Posts: 35,065
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From: Bergen County, NJ Democrats, doing for the country what they did for Michigan
You could, but I'd measure both sides. Design is to maintain average head pressures of 200 psi (between about 70 and 90 degree ambients) and the low will fall into place. Now if you live where summer temps routinely exceed 100, you might pay particular attention to low; ie, aim for a slight undercharge - say no more than 35 psi on the low if the outside air is 100. This may make it a few degrees better at the vents (high 50's instead of low 60's) but it's going to cycle a lot more when it's below 70 which leads to more wear and tear.