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AC compressor question
- Thread starter darek_u
- Start date
Usually this information is given in the car manual but it's not the case with W124... I'm trying to figure out if my AC works properly after refilling with R134 but ambient temp is 5 deg. C so I'm afraid I can be on the edge. Different car makers give different minimum ambient temps, for my Porsche it is 3 deg. C, for my daily driver 4 deg. C for example.
My experience with W124, E320, 1994-5, indicates that outside temperature is not a factor for the AC compressor. However, the coolant temperature is. When the coolant temperature is too high, it shuts off the AC compressor and the turns on the auxilary cooling fans. One of the temperature sensors on the water pump is used for this purpose.
500E is a different animal to me so my experience might be irrelavent.
jftu105
500E is a different animal to me so my experience might be irrelavent.
jftu105
Thank you, this may be the culprit, it is just too cold...
Hahahaha! No but I know many of them
Had to deal with AC lately. For any AC diagnosis, a set of AC gauges are very useful. It is really important to measure both high and low pressures. The AC compressor could be shut off due to pressure too low or too high or freon temperature too high (cycling).
I have experienced twice of AC not running, not due to freon leak, but due to restriction, most likely at the expansion valve. This is a consequence of using SUPERSEAL, which is the sealant to repair leaks.
The evaporator of W124 is known to develop leaks. When that happens, eventually, all R134A will leak out and the system cannot hold vacuum. Removing the entire dash to replace the evaporator is an enormous job that I will never be able to do. The alternative is to put sealant in, about $30 a can, and pray. In fact, this type of sealant is highly effective and I have used it to fix home AC too.
The downside of using sealant is that it could cause restriction in the AC loop. It is very important that your AC system is completely free of moisture because the sealant is activated by moisture. A good dryer is important.
When the AC restriction happens, the high pressure will keep building up, even up to nearly 500 psi, while the low pressure side could be normal, low, or high. When the high pressure side is too high, the compressor cannot pump anymore. It would be shut off by the pressure switch. If you short the pressure switch to force the compressor clutch to engage, the serpentine belt would slip, giving out squeaking noise or burn with smoke.
Therefore, if you have a set of gauges to measure both high and low pressures, you will immediately detect this clogging problem. If one only measures the low pressure port, one could mistakenly think the problem as low in freon. Continue to charge would be problematic.
jftu105
I have experienced twice of AC not running, not due to freon leak, but due to restriction, most likely at the expansion valve. This is a consequence of using SUPERSEAL, which is the sealant to repair leaks.
The evaporator of W124 is known to develop leaks. When that happens, eventually, all R134A will leak out and the system cannot hold vacuum. Removing the entire dash to replace the evaporator is an enormous job that I will never be able to do. The alternative is to put sealant in, about $30 a can, and pray. In fact, this type of sealant is highly effective and I have used it to fix home AC too.
The downside of using sealant is that it could cause restriction in the AC loop. It is very important that your AC system is completely free of moisture because the sealant is activated by moisture. A good dryer is important.
When the AC restriction happens, the high pressure will keep building up, even up to nearly 500 psi, while the low pressure side could be normal, low, or high. When the high pressure side is too high, the compressor cannot pump anymore. It would be shut off by the pressure switch. If you short the pressure switch to force the compressor clutch to engage, the serpentine belt would slip, giving out squeaking noise or burn with smoke.
Therefore, if you have a set of gauges to measure both high and low pressures, you will immediately detect this clogging problem. If one only measures the low pressure port, one could mistakenly think the problem as low in freon. Continue to charge would be problematic.
jftu105
FYI... there are several different Cliplight Super Seal products. The top-of-the-line offering, previously called "Total Auto" and currently named "Platinum", includes a drying agent to help reduce problems with moisture. Part number is "976KIT", link below, photos here.
Of course it's best to use a proper AC system vacuum pump (not a venturi vacuum generator) to boil off moisture first, and also confirm the system will hold vacuum to the minimum standards mentioned in the instructions - see attached PDF.
You are absolutely correct that both low and high pressures need to be checked. High side pressures over 300 generally indicate something is wrong. The safety cutout kills the compressor at 30 bar (435 psi) and will allow the compressor to turn on again when pressure drops below 22 bar (320 psi). The electric fans turn on at 16 bar (230 psi) and turn off at 12 bar (175 psi). This means the low speed fans do not ALWAYS run when the compressor is running; in cool temps the pressures may not be high enough to engage the fans. Interestingly, FSM job 83-544 indicates the gauges may read 2 bar/30 psi higher than actual pressure at the switch; but I've not observed this personally.
While pressures will vary based on charge level and ambient temps... I've found on good 124 systems with factory R-134a (1992-95), in ambients around 80-90F, low pressure will generally be in the 10-30psi ballpark, and high side in the upper 100's to lower 200's. Higher ambients will increase those pressures. Ideally the compressor will cycle on & off as vent temps dip below 45°F, preferably on high fan speed, although it may be necessary to drive the car at 30+mph to get the compressor cycling on hot days.
The expansion valve replacement is a miserable job. Best to practice on a junkyard car if possible, if you've never done it before.
Of course it's best to use a proper AC system vacuum pump (not a venturi vacuum generator) to boil off moisture first, and also confirm the system will hold vacuum to the minimum standards mentioned in the instructions - see attached PDF.
You are absolutely correct that both low and high pressures need to be checked. High side pressures over 300 generally indicate something is wrong. The safety cutout kills the compressor at 30 bar (435 psi) and will allow the compressor to turn on again when pressure drops below 22 bar (320 psi). The electric fans turn on at 16 bar (230 psi) and turn off at 12 bar (175 psi). This means the low speed fans do not ALWAYS run when the compressor is running; in cool temps the pressures may not be high enough to engage the fans. Interestingly, FSM job 83-544 indicates the gauges may read 2 bar/30 psi higher than actual pressure at the switch; but I've not observed this personally.
While pressures will vary based on charge level and ambient temps... I've found on good 124 systems with factory R-134a (1992-95), in ambients around 80-90F, low pressure will generally be in the 10-30psi ballpark, and high side in the upper 100's to lower 200's. Higher ambients will increase those pressures. Ideally the compressor will cycle on & off as vent temps dip below 45°F, preferably on high fan speed, although it may be necessary to drive the car at 30+mph to get the compressor cycling on hot days.
The expansion valve replacement is a miserable job. Best to practice on a junkyard car if possible, if you've never done it before.
Super Seal Platinum™
Permanently seals & prevents leaks in mobile A/C systems, Eliminates moisture & prevents acid formation, UV dye highlights larger leaks.
www.cliplight.com
To deal with the clogging problem, I replaced the expansion valve once. It was a miserable job due to tight space and potential rounded allen bolt to hold the expansion valve. In fact, the bolt was rounded and it took me a long while, using various extractors, to finally got it out.
There is a little trick to fix the clogging temporally but I am not liable to any dangers it might cause. TRY AT YOUR OWN RISK.
When the high pressure is too high due to clogging, this pressure will not reduce significantly even after a long while, especially in a hot day. Even after the pressure drops after some time, the compressor would quickly raise it up again, and shut off.
The little trick is to release the pressure manually.
CAUTION ALERT!!!
Wear glove and use a philip screw driver or something similar. Open the high pressure port cover. Put your face away from the engine area. Reach down, forcefully press down the high pressure port valve stem. A short burst of freon will shoot out. You may try it again. Only allow a short burst, each time.
If you have a set of gauge manifold, then you could do this much easier. You can even recover the freon with an empty freon can.
Sorry ozone layer. We use R134A for good reasons.
This burst of release will drastically reduce the pressure and possibly creates a backflow to unclog the AC loop. As a result, your AC might run again.
Use this trick only when you are stranded on the road in a hot day without AC. Otherwise, do proper repair to clean up the clog, vacuum, and recharge.
jftu105
There is a little trick to fix the clogging temporally but I am not liable to any dangers it might cause. TRY AT YOUR OWN RISK.
When the high pressure is too high due to clogging, this pressure will not reduce significantly even after a long while, especially in a hot day. Even after the pressure drops after some time, the compressor would quickly raise it up again, and shut off.
The little trick is to release the pressure manually.
CAUTION ALERT!!!
Wear glove and use a philip screw driver or something similar. Open the high pressure port cover. Put your face away from the engine area. Reach down, forcefully press down the high pressure port valve stem. A short burst of freon will shoot out. You may try it again. Only allow a short burst, each time.
If you have a set of gauge manifold, then you could do this much easier. You can even recover the freon with an empty freon can.
Sorry ozone layer. We use R134A for good reasons.
This burst of release will drastically reduce the pressure and possibly creates a backflow to unclog the AC loop. As a result, your AC might run again.
Use this trick only when you are stranded on the road in a hot day without AC. Otherwise, do proper repair to clean up the clog, vacuum, and recharge.
jftu105
ClipLight is a wonderful product. I've saved several W140 and W124 evaporators with this stuff. It's not a be-all to end all, but if the leak hasn't gotten excessive it will do a great job.
I had a W124 E300D that it held for over two years before the leak got to the point where it couldn't seal it. Being that I'm in Florida, that's pretty darned good for $35 worth of material versus an evaporator replacement.
Dan
I had a W124 E300D that it held for over two years before the leak got to the point where it couldn't seal it. Being that I'm in Florida, that's pretty darned good for $35 worth of material versus an evaporator replacement.
Dan
I simply use Superseal, available from most auto parts store. In one case, I had to use two cans and, after fully charged, got on highway to run the AC really hard to seal it. The freon was still rushing out through the vent initially and then it stopped. It has been fine since, over 7 years ago. I did have to deal with the clogging issue later.
jftu105
jftu105
OHHHHHHHHHHH. That is not the same as Cliplight-brand Super Seal. Different products.
I'm assuming you used Interdynamics or A/C Pro brand "Super Seal", which appears to be available at most FLAPS / McParts stores.
Cliplight 976KIT is much harder to find and costs 3x as much.
Typically, the Superseal I got from Walmart is about $25. One day, I saw a discount store selling it for $5.00 each. I bought all I can find in that store, about 7 or 8 of them. Here is the links to Walmart and Autozone. For home AC treatment, I went for the cliplight brand at $50 to $60 a shot.
jftu105
jftu105
A/C Pro Super Seal A/C Stop Leak Treatment (3 ounces) - Walmart.com
Buy A/C Pro Super Seal A/C Stop Leak Treatment (3 ounces) at Walmart.com
www.walmart.com
A/C Pro ACP-105V R134a with Max Seal Refrigerant 12oz
Shop for A/C Pro ACP-105V R134a with Max Seal Refrigerant 12oz with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.
www.autozone.com
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