Year: 1972
Make: chevy
Model: chevelle
Engine Size: 350
Refrigerant Type: R12
Ambient Temp: 90
Pressure Low: 30-37
Pressure High: 275-300
Country of Origin: United States
Hope someone can help me out with the Chevelle, the wife wont go anywhere with me in this heat until this AC works right. I don't know much about A/C other than my research on here, but I have this equipment (Snap On ACT 3120 R12 automatic servicing machine) for my airplanes. Here goes.
History on the system= I was told it worked when I bought it, but the compressor didn't come on and it didn't blow cool air, I assumed the system was bad, but when I pushed the valve cores in the high and low side it had pressure, so I hooked up the R12 machine, put 4 lbs in and the compressor kicked on and quickly frosted up the low side........ I verified the POA was stuck with your guys info, ordered and replaced it with the POA update kit from Old Air. I checked the oil in the compressor (10 oz or so), changed the receiver/dryer, I evacuated the system to -25 PSI, it held for 20 minutes dropping to -23 PSI. I then serviced up the system with 4.5 lbs of R-12. With the car idling at around 1500 RPM, I adjusted the switch on the update kit to kick on the compressor @ 37 PSI and off @ 30 PSI (low side) per the instructions. Meanwhile the high side moves back and forth between 275 and 300 PSI during the cycling. The air blows cool (65 deg on a 90 deg day), but I would expect cooler. Is there anything else I can check or do? Is this normal? I have inspected the condenser with the grill off the car and it appears perfect. If the car holds vacuum I have no leak...right?
Thanks for any help or info. Joe
Your vacuum is not enough. You need -29 on the vacuum. Your high side is to high. Could be from a few things such as: Poor airflow across condenser, bad fan clutch, non-condensables (highly probable due to vacuum level you listed). You may have adjusted the cycling on the low side to compensate for the high highside.
The machine does the vacuum automatically, I cant see in the directions how to adjust it. I didn't have a fan in front of the car. I will replace the fan clutch since I think its original.
Well today went out and started the car up with the gauges still on from yesterday. Found low side the same, high side had fallen to 175-200 during the cycling. Does this indicate a leak? Its about 10 deg cooler today (80 deg). Also during the drive it was only blowing really cold air when I wasnt moving or at slow cruising. During 35mph + the air was just cool.
I would get the machine back on it & suck the r12 out while it was still there.
What are you using for an expansion device?
If you are working on aircraft A/C, you should absolutely be using a micron gauge during evacuation.
If you did not already, put some dye in the system before you charge it again. Do you own a sniffer?
B.
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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
I guess I need laymans terms here. What is an expansion device? By micron gauge do you mean filterwise? No on the dye and sniffer. The system in the aircraft is a typical Chrysler system from the 70's, never gave me a problem to worry about.
I concur with most of the other posts. Your vacuum is a bit "high" (depends on how you look at it) but I see other issues in your post.
1. If it is dropping at all there is a leak. It is obviously a small one so may or may not be an issue down the road. The bigger issue is if it is leaking on the vacuum that means air in the system before the charge. So high side will be high and it will not cool as well as it could.
2. The POA update kit works differently than the POA valve. As such as the evap pressures climb it effects the opening of the expansion valve and causes it to close down. This is opposite of what you want to happen if the Evap pressures and temps are on the high side. Hi low side pressures indicate you are not completely "flooding" the evap with liquid or you are over/under charged. All will cause a lack of cooling.
3. The original system called for 4 1/8 LBs. of R12. you indicated you added 4 1/2. This is positively an over charge. And it will cause a lack of cooling.
I have several questions you may or may not be able to answer.
1. What is the temp of the condenser outlet
(actually the tube leading from the receiver/drier to the expansion valve is close enough)?
2. What is the temp of the outlet of the evaporator?
(slide your thermometer inside the rubber seal at the outlet opening in the case)
3. What fan speed are you setting the low side switch at?
(If the load is high it should never cycle on hi blower. This should be set at the lowest blower speed. With the blower on high and 85 to 90 degree ambients most time it should not be able to cycle do to the load on the system. If it is cycling I would guess you have a restriction in the high side or the expansion valve is closing down too much for effective cooling.)
4. What is the temperature of the air entering the condenser?
(check this at 2 to 6 inches in front of the condenser with your thermometer. It would be better to have a "wet bulb" and a "dry bulb" for this testing but .......)
The OEM expansion device for that system is a TXV or thermostatic expansion valve. It meters refrigerant into the evaporator based on the evaporator discharge line temperature.
Some aftermarket conversions replace the TXV with a simple orifice tube.
A micron gauge is a very sensitive vacuum gauge. You really want to pull a system down to the 400 to 1000 micron range. "29" on the average gauge is about 50,000 microns...
A "chrysler system" ? on what type of aircraft? And I thought the junk on the Queen Air was archaic.
B.
-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
If you did not pull the TXV when you serviced the system, that may be one of your problems. A partially blocked or malfunctioning TXV can cause poor performance.
A Falcon 10? not surprised I guess. It is French. Lucky for you Citroen was not making the A/C for them.
B.
-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
Some of the older vehicles had a filtering screen on the input of the TXV. Many opinions were to remove the screen and trash it. Also, when you disassemble the system and remove the TXV, note the location of the sensing bulb. If the line is 7/8 in or smaller, mount the bulb horizontally on top or to the 1 o'clock position. If the line is larger than 7/8 in mount the bulb at 3 to 4 o'clock position. Insulate the bulb with cork prestolite tape.
To check your fan clutch, spray a water mist on the condenser. If the high side drops dramitically, there is your problem...air flow. Cure that and then readjust your cycling points.
Is the TXV the expansion valve?
Today my pressures are the same as yesterday, and this system is blowing ice cold in the garage, but above 35mph it is just cool. I'm going into the heater box next. I think the internal doors are not functioning correctly since I only have cold air blowing out the floor vents. There appears to be no vacuum to the dash. Maybe the heater core air is mixing.
btw, spraying the condenser had NO effect on the high side
Found the main vacuum line to the A/C controls pinched between the heater box and the firewall, I now have all the correct functions!! But I found out the door between the heater core and evaporator is on the cable. So I'll still have to take it for a drive to see if the A/C warms up at speed still.
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