My A/c has been working Ok up until last week, cold air output began to drop and now I have no cold air. I borrowed a set of gages and the system is showing 70 psi on the high side and the low side without the engine running. After starting the engine and running the a/c on high i'm getting over 400 psi on the high side and over 100 psi on the low side. Eventually the pressure will go over 450 psi and the clutch on the compressor will slip. I shut it off at that point. Is this condition caused by a clogged orfice tube. I changed to 134a over 3 years ago and haven't had any problems until now. Any suggestions?
A/C running @ over 400 PSI
- Thread starter The Car Whisperer
- Start date
- Thread starter
- #2
The engine fan comes on. This pressure only takes about 2 to 3 minutes to build after I start the engine. How do you check for a clogged condenser? I have a gage set I can use if thats what's needed to check it. The pressure will fluctuate, goes high and then it drops, the low side just seems to stay around 100 psi, fluctuating slightly with the high side fluctuation.
M
Magmotor
Guest
I hope you ment 450 kPa. If it's PSI, I'd run like.....maybe the attached chart will help out some. 
F
FordNoMore!
Guest
Yes , if you have a restriction your suction side(low)will be very low or vaccum, and your Liquid side(high) will be very high, your pressures lead me to think that either your coil is plugged, with a suction pressure that High and a head that high almost sounds like it is overcharged, but if it hasnt been touched in 3 yrs, then I guess that cant be the case, investigate the coil area in front underneath the nose of the car for obstruction, if possible blow out with air, or water stream,good luck
- Thread starter
- #5
Ok, like it says on most things related to air conditioning - "For Professional Use Only". Since I am not a pro, just an overly serious ameture, I admit that I read the wrong scale on the gage set. Evidently you need to read the scale for the appropriate refrigerant in the system. After discovering this I went out and took some new readings in the past hour.
Ambient temperature 76 deg F, High side and low side pressure at 65 psi with engine cold and not running. I started up the engine and turned the AC on max with fan on high. pressure goes right up up to 182 psi on the high side and down to 50 psi on the low side, but pressure keeps rising on both sides until high side goes over 250 and then the clutch will start to smoke for a second and disengage. The pressure imediately drops on the high side to 100 psi and thlow side rises to 100 psi. Numbers are approximate because the needles realy fluctuate rapidly at this point. Then the clutch engages again and the cycle starts over. The first cycle when the AC is turned on begins to put out about 64 deg F air at the center vent, then after the first cycle complets and the clustch engages for the second cycle the air temp from the center vent goes over 80 deg F and thats about when the pressure goes off the scale and the clutch begins to smoke for a second or 2 before it disengages. I want to repair this correctly and not have to go inthere again later. Is it OK to just unplug the compressor for now until I can do a proper repair. I want to stick with the R134a because it is environmentally friendly. I did check the condensor and it was free of debris and the fans do come on at 200 deg F and off at 180 deg F. I know this is the place to get all the right answers!
Ambient temperature 76 deg F, High side and low side pressure at 65 psi with engine cold and not running. I started up the engine and turned the AC on max with fan on high. pressure goes right up up to 182 psi on the high side and down to 50 psi on the low side, but pressure keeps rising on both sides until high side goes over 250 and then the clutch will start to smoke for a second and disengage. The pressure imediately drops on the high side to 100 psi and thlow side rises to 100 psi. Numbers are approximate because the needles realy fluctuate rapidly at this point. Then the clutch engages again and the cycle starts over. The first cycle when the AC is turned on begins to put out about 64 deg F air at the center vent, then after the first cycle complets and the clustch engages for the second cycle the air temp from the center vent goes over 80 deg F and thats about when the pressure goes off the scale and the clutch begins to smoke for a second or 2 before it disengages. I want to repair this correctly and not have to go inthere again later. Is it OK to just unplug the compressor for now until I can do a proper repair. I want to stick with the R134a because it is environmentally friendly. I did check the condensor and it was free of debris and the fans do come on at 200 deg F and off at 180 deg F. I know this is the place to get all the right answers!
- Thread starter
- #6
The clutch engages and disengages ok, it only slips for a second or 2 when the pressure gets extremely high. It appears to be the original compressor and it is approaching 18 years old so I wouldn't doubt that it could be on its way out though.
If I choose to replace the compressor I want to replace it with a new one, not rebuilt. Does anyone on this forum have any suggestions for a source for a new compressor that is compatable with R134a? If I replace the compressor should I also replace the accumulator, condensor and expansion orfice.
I don't have any detectable leaks, the static charge pressure has remained the same 70 psi for the past 3 years so I think the system is tight otherwise.
If I choose to replace the compressor I want to replace it with a new one, not rebuilt. Does anyone on this forum have any suggestions for a source for a new compressor that is compatable with R134a? If I replace the compressor should I also replace the accumulator, condensor and expansion orfice.
I don't have any detectable leaks, the static charge pressure has remained the same 70 psi for the past 3 years so I think the system is tight otherwise.
HPG
Well-known member
Just went through an A/C job on my 88. Clutch was bad. Rather than spend $180 for a clutch, and find out the compressor was bad and ruined the new clutch, I replaced the compressor. $425 for the compressor. Actually, I think you may have a restriction in the high side of the system. A system flush may take care of this befor you change the compressor. If the pressure equalized after shutting off, the orfice tube is not plugged. Good Luck
- Thread starter
- #8
How do you flush the system? If I replace the compressor and the accumulator I would like to do the job the absolute best way it can be done. I would want to flush the condensor and evaporator to make sure everything is clear in those parts before putting in a new compressor etc. Did you put in a new or rebuilt compressor. Where did you get it? If I get a new GM compressor it probably will not be compatable with the R134a.
kalmwill
Active member
One of the things that you have to watch for when converting to R134a is that system isn't overcharged. The quantity of R134a coolant is 80% of that of R-12. I have had a compressor in another car where, in hot weather, the pressure built up to such an extent that the compressor wouldn't turn and caused severe belt squeeling due to slippage. The correct amount of coolant is important. Also the accumulator should be replaced whenever you open up the system. It is a small price to pay to keep the moisture out.
M
Markyman
Guest
Have you checked the expantion screen and orf.
Robertwav1
Well-known member
Just wish to point out that head pressure and suction pressure on the rise like that indicates to me ... since all other avenues were covered here ... that you have a fan problem. Are you sure it's turning fast enough to cool the head pressure? Apparently you didn't add gas since the system was working correctly right? No chance for air then if this is the case. The pressures you indicate do not suggest a blockage in the system. Evacuate it and recharge first after you confirm condenser cooling...go from there. Also....wish to point out that although 134a is enviorment friendly...it's NOT safe to be exposed to this gas. In fact...it's worse then 12 when it comes to human exposure. Please don't breathe it in. I'm involved in a refrigeration forum discussing this matter and just wish to point out to everyone that studies have been made on this topic. Be safe and understand what your working with.
- Thread starter
- #12
Thanks for all the help, I'm going to evacuate the system, flush and recharge and see what happens. I'll let you know what happens.
F
FordNoMore!
Guest
High suction and low discharge pressure, Bad valves!!,new Compressor time.
T
tedster
Guest
If you're getting 400+psi on the high side, there ain't nuthin' wrong with the valves in your compressor! Way too many compressors are replaced when there is nothing wrong with them. You can do this and replace some other stuff, too, and it'll probably be fine, but do you want to know what is really going on?
Clogged air passages on the condenser will make head pressure rise slowly. Same with non-functional fans.
A plugged orifice WILL cause the high side pressure to rise rapidly. And while , in theory, the suction side should go to vacuum, everyone seems to be forgetting that there is usually about 0.5 lbs of excess refrigerant in liquid form held in the accumulator. That liquid evaporates and keeps the low side pressure up, even though there is little to no flow returning.
Based on your description, the clutch is being disengaged due to the high pressure cut-off switch being triggered long before that excess charge is used up.
Evacuate (using proper reclamation equipment, please), and pull the orifice before spending lots of cash. The big concern is, what has plugged the orifice? There shouldn't be any debris, but if there is, it is likely that the compressor is goin' south due to wear/lack of proper oil circulation. Dark sludge is commonly observes when aluminum particles start mixing with the PAG oil used with R134a.
I'll bet that is what you'll find. If so, you'll need to flush the system to remove debris/sludge form the lines and heat exchangers. You may want to replace the accumulator because after 17+ years, the dessicant is probably used up. The desiccant absorbs moisture that, try as you might, you cannot evacuate.
Hope this helps.
Tedster
Unfortunately, I AM an A/C professional, and as such
PAID
I'M
WORKED
Clogged air passages on the condenser will make head pressure rise slowly. Same with non-functional fans.
A plugged orifice WILL cause the high side pressure to rise rapidly. And while , in theory, the suction side should go to vacuum, everyone seems to be forgetting that there is usually about 0.5 lbs of excess refrigerant in liquid form held in the accumulator. That liquid evaporates and keeps the low side pressure up, even though there is little to no flow returning.
Based on your description, the clutch is being disengaged due to the high pressure cut-off switch being triggered long before that excess charge is used up.
Evacuate (using proper reclamation equipment, please), and pull the orifice before spending lots of cash. The big concern is, what has plugged the orifice? There shouldn't be any debris, but if there is, it is likely that the compressor is goin' south due to wear/lack of proper oil circulation. Dark sludge is commonly observes when aluminum particles start mixing with the PAG oil used with R134a.
I'll bet that is what you'll find. If so, you'll need to flush the system to remove debris/sludge form the lines and heat exchangers. You may want to replace the accumulator because after 17+ years, the dessicant is probably used up. The desiccant absorbs moisture that, try as you might, you cannot evacuate.
Hope this helps.
Tedster
Unfortunately, I AM an A/C professional, and as such
PAID
I'M
WORKED
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