Low side A/C pressure too high?
Thread Starter
Racer
Joined: Nov 2010
Posts: 253
Likes: 34
From: Central Va
Great info everyone - I apppreciate it. It does make sense that after an engine pull, it would not be as it was when it was flushed and converted a couple of years ago. I still want to get the readings of course, if nothing else than for my own knowledge as I am learning more about this.
Then consider the evacuation in order to get any lingering air/ater out and refill by weight. (80-85% of the R12 spec). I hear AutoZone lends out gauges for free, I might check that out or just buy a set.
Then consider the evacuation in order to get any lingering air/ater out and refill by weight. (80-85% of the R12 spec). I hear AutoZone lends out gauges for free, I might check that out or just buy a set.
Rennlist Member
Joined: Jun 2005
Posts: 3,261
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From: Park Ridge, IL (near Chicago)
Do some research about the correct way to attach the hoses. The high pressure hose is a little scary for me. Make sure you understand how the gauge valves work or you can have 300 PSI in your 12 0z. can of freon. Not good.
Best of luck,
Dave
Best of luck,
Dave
Thread Starter
Racer
Joined: Nov 2010
Posts: 253
Likes: 34
From: Central Va
Ok, finally have the gauges, after finding out that the guy that did the conversion, left the high side with the old connector, so had to go back to the store get that....
Ambient air temp - 80
Humidity - 81
High side - 175
Low side - 25
Car is warm (not hot but warmed up from idle)
Is blowing around 60+ degrees
Notes - low side reading I suspect is much lower because I lost some pressure playing with the high side connector which is hard to get to by the receiver/dryer in front of the condenser coils
The generic charts I see around say that at 80 degrees low should be mid 40s and high 175 to 210. Most if the comments about our system center around 30.
Anyway, it sure is not overcharged anymore, is the sweet spot 30 or 40 for the low side and 210 or 225 for the high? Blowing 60 indicates it is a little low at least. I understand there could be water vapor and air in the system making it more inefficient.
The next step would be to get is completely evacuated and recharged properly.
For now I would like to decide on the target numbers if possible.
Ambient air temp - 80
Humidity - 81
High side - 175
Low side - 25
Car is warm (not hot but warmed up from idle)
Is blowing around 60+ degrees
Notes - low side reading I suspect is much lower because I lost some pressure playing with the high side connector which is hard to get to by the receiver/dryer in front of the condenser coils
The generic charts I see around say that at 80 degrees low should be mid 40s and high 175 to 210. Most if the comments about our system center around 30.
Anyway, it sure is not overcharged anymore, is the sweet spot 30 or 40 for the low side and 210 or 225 for the high? Blowing 60 indicates it is a little low at least. I understand there could be water vapor and air in the system making it more inefficient.
The next step would be to get is completely evacuated and recharged properly.
For now I would like to decide on the target numbers if possible.
Chronic Tool Dropper
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From: Bend, Oregon
Your car came with a sight-glass in the top of the receiver-drier. With the system running and engine at ~1500 RPM, fan set on "2", look at that glass and see what the flow looks like. With your low pressures it's probably close to all vapor. Your target is close to all liquid, keeping the pressures in check on the way.
For your ambient conditions, I'd be comfortable with 225 hi side, and up to 40 low side, and still with bubbles in the sight glass. Remember that air in the system never condenses, so gives you false comfort that what you see in the glass is OK. Keep an eye on high-side pressures, since they will run away quickly when condenser capacity is insufficient due to air inside or poor shedding of heat outside from airflow issues.
With the car not running and everything cold (like first thing in the morning before starting the engine), get an ambient temp reading and look at your low-side gauge. See if the temp on the R-134a ring where the needle is pointing matches what you are seeing on the thermometer. This might give you a broad-brush indication of what the partial pressure of air is in your system. If the error is more than a pound or maybe a couple degrees higher than the the thermometer reading, you are spinning your wheels trying to get the system really cold.
There's a lot to be learned from one of the generic refrigeration manuals from Chiltons or similar. Tons of system safety issues to consider.
For your ambient conditions, I'd be comfortable with 225 hi side, and up to 40 low side, and still with bubbles in the sight glass. Remember that air in the system never condenses, so gives you false comfort that what you see in the glass is OK. Keep an eye on high-side pressures, since they will run away quickly when condenser capacity is insufficient due to air inside or poor shedding of heat outside from airflow issues.
With the car not running and everything cold (like first thing in the morning before starting the engine), get an ambient temp reading and look at your low-side gauge. See if the temp on the R-134a ring where the needle is pointing matches what you are seeing on the thermometer. This might give you a broad-brush indication of what the partial pressure of air is in your system. If the error is more than a pound or maybe a couple degrees higher than the the thermometer reading, you are spinning your wheels trying to get the system really cold.
There's a lot to be learned from one of the generic refrigeration manuals from Chiltons or similar. Tons of system safety issues to consider.
Thread Starter
Racer
Joined: Nov 2010
Posts: 253
Likes: 34
From: Central Va
Excellent dr bob. I have certainly learned a lot in one week! It has been fun. Now I think I have a pretty good handle on this as a start, at least.
Thanks to everyone for the good advice. Funny,,,, today after the rain came... it is 75 degrees, no bugs, no wind, no rain.....DRIVING weather! Now I did not need the A/C .....!
Thanks to everyone for the good advice. Funny,,,, today after the rain came... it is 75 degrees, no bugs, no wind, no rain.....DRIVING weather! Now I did not need the A/C .....!
Former Vendor
Joined: Feb 2005
Posts: 15,228
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From: Anaheim
Hey all,
My A/C was working cool prior to my recent engine pull. But afterwards, it would only keep up if you went from a cooler garage into this sweltering heat we have had here lately. If you stopped in the sun and left it and then started back up, no way could it cool the car down.
I checked the low side pressure and it was less than 30 PSI. (like 1/2)
So I added one can of coolant (has been converted to 134a previously). It was my first time to doing this and I neglected to watch the pressure as it went in. The whole can went in fine. And cold air blows immediately now.
Afterwards I checked it again after a complete disconnection and test run. The low side now reads 40 PSI. Is that too much, or am I ok at this reading? I suppose I could bleed some out if needed.
By the way - the Low side for an 83 is on the passenger side below the fender, pointing towards the fuel rail. I had no cap on mine and the high side had no color on the cap (in front of the radiator near the dryer). The Low side is a larger tube and had obviously been disturbed (hence the cap missing!)
Anyway any comments welcome.
My A/C was working cool prior to my recent engine pull. But afterwards, it would only keep up if you went from a cooler garage into this sweltering heat we have had here lately. If you stopped in the sun and left it and then started back up, no way could it cool the car down.
I checked the low side pressure and it was less than 30 PSI. (like 1/2)
So I added one can of coolant (has been converted to 134a previously). It was my first time to doing this and I neglected to watch the pressure as it went in. The whole can went in fine. And cold air blows immediately now.
Afterwards I checked it again after a complete disconnection and test run. The low side now reads 40 PSI. Is that too much, or am I ok at this reading? I suppose I could bleed some out if needed.
By the way - the Low side for an 83 is on the passenger side below the fender, pointing towards the fuel rail. I had no cap on mine and the high side had no color on the cap (in front of the radiator near the dryer). The Low side is a larger tube and had obviously been disturbed (hence the cap missing!)
Anyway any comments welcome.
This car should have a sight glass in the dryer....and regardless of the type of Freon used, you should have a solid stream of Freon there.
If you went from not properly cooling to cold air, with one can of Freon....very doubtful that you have overcharged the system by much, if any.....it'a not even a pound.
And unless you are charging a system underwater....the amount of moisture in the charging hose is moot....that is what the dryer is for.
R134 in an old system designed for R12 is going to leak out fairly quickly....past the non-barrier hoses and out the o-rings not intended for R134.....so even if the system is slightly overcharged, it will "self-correct" pretty quickly.
Relax and have a beer.
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Chronic Tool Dropper
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From: Bend, Oregon
Reading the sight glass as a sole indication of charge is not ideal. The quality of the liquid stream in the glass varies as ambient temperature, engine speed and heat load (amount of heat actually removed from the cabin) change. It's a "yardstick" indication, and when used with pressures and temperatures, can give you an idea of how the system is performing. Synopsis: Don't rely just on the sight glass.
