need some help with A/C
Thread Starter
Pro
Joined: Nov 2012
Posts: 672
Likes: 0
From: Chesapeake Virginia
need some help with A/C
Hey guys, now that I'm about done with the rebuild I figured I'd get the A/C charged up and running. but I seem to have an issue I need some input on.
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Hey guys, now that I'm about done with the rebuild I figured I'd get the A/C charged up and running. but I seem to have an issue I need some input on.
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
This ensures that the fan is fully engaged and pulling air through the condenser. Also ensure that the RPMs are around 1000 or so for good air flow.
If you have insufficient air through the condenser what you will see is high on high side and low on low side because you don't have enough freon in yet due to your concern with the high side pressure.
If electric fans make sure they are running.
Once you get the system filled your compressor will continue to run.
Right now it sounds like the low side switch is kicking it off due to low pressure then the low side pressure rises while it's off and allow the switch to run the compressor again until pressure is too low again and repeated over and over.
Just filled my 77 yesterday. Initially my cooling fans were not running and saw exactly what you're looking at.
I also put a digital thermometer in the air duct to see how cold it's getting. I got 43* yesterday with 70* ambient temps.
Ensure that A/C selector is in max.
Last edited by REELAV8R; May 20, 2014 at 03:34 PM.
Instructor
Joined: Jun 2012
Posts: 192
Likes: 0
Hey guys, now that I'm about done with the rebuild I figured I'd get the A/C charged up and running. but I seem to have an issue I need some input on.
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
here's the deal:
100% new system (comp, hoses, o-tube, evap, conden, drier, low pressure switch)
recharging with R-12, vacuumed down to 30 hg and let the vacuum pump run for about an hour, then let it sit for an hour with no leaks.
charged with the right amounts of oil in the compressor and drier.
charged with 48 oz. of r-12
ambient air temp 70*
suction side pressures 40 psi (compressor off)--down to 25 psi (compressor running)
high side pressure 250 psi compressor running.
air is cool but not cold as it should be
the condenser is sealed to the core support good, running a new clutch fan.
the high side pressures seem real high to me ??
the compressor cycles on and off (about 50/50 cycle), shouldn't it run all the time ??
Thread Starter
Pro
Joined: Nov 2012
Posts: 672
Likes: 0
From: Chesapeake Virginia
does anyone know what the charge amount for the system is (R12), I tried searching for it but all I can find is info about converting to 134a. I saw one post that said between 2.75 and 3.00 lbs = 48oz. but I'm not sure if thats even close.
Burning Brakes
Joined: Feb 2011
Posts: 849
Likes: 0
From: Woodland California
If you are running the stock clutch fan make sure the engine is up to full temp with hood down before you start.
This ensures that the fan is fully engaged and pulling air through the condenser. Also ensure that the RPMs are around 1000 or so for good air flow.
If you have insufficient air through the condenser what you will see is high on high side and low on low side because you don't have enough freon in yet due to your concern with the high side pressure.
If electric fans make sure they are running.
Once you get the system filled your compressor will continue to run.
Right now it sounds like the low side switch is kicking it off due to low pressure then the low side pressure rises while it's off and allow the switch to run the compressor again until pressure is too low again and repeated over and over.
Just filled my 77 yesterday. Initially my cooling fans were not running and saw exactly what you're looking at.
I also put a digital thermometer in the air duct to see how cold it's getting. I got 43* yesterday with 70* ambient temps.
Ensure that A/C selector is in max.
This ensures that the fan is fully engaged and pulling air through the condenser. Also ensure that the RPMs are around 1000 or so for good air flow.
If you have insufficient air through the condenser what you will see is high on high side and low on low side because you don't have enough freon in yet due to your concern with the high side pressure.
If electric fans make sure they are running.
Once you get the system filled your compressor will continue to run.
Right now it sounds like the low side switch is kicking it off due to low pressure then the low side pressure rises while it's off and allow the switch to run the compressor again until pressure is too low again and repeated over and over.
Just filled my 77 yesterday. Initially my cooling fans were not running and saw exactly what you're looking at.
I also put a digital thermometer in the air duct to see how cold it's getting. I got 43* yesterday with 70* ambient temps.
Ensure that A/C selector is in max.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
When you top a system you don't determine how much is missing and add it for a certain total, same here.
The listed amount just gives you an idea about how much it should take.
except with electric fans they should run when ever the AC in on,
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
R12 system is easy to tell when full, watch the sight glass, you should only see an occasional bubble going past when its been running and stabilized. Seems like you have an air flow problem across the condenser, you might try spraying it with a garden hose and see if your hi side pressure comes right down.
Thread Starter
Pro
Joined: Nov 2012
Posts: 672
Likes: 0
From: Chesapeake Virginia
thanks guys, I'll try the garden hose idea, unfortunately there is no sight glass on the '81 so it's a bit more difficult.
I hate to keep throwing freon in it, this stuff aint cheap and I would rather not be wastefull and overfill it. I'll put in what I have to but need to do it in a controlled fashion
I hate to keep throwing freon in it, this stuff aint cheap and I would rather not be wastefull and overfill it. I'll put in what I have to but need to do it in a controlled fashion
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