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Update at bottom: Another A/C problem (car this time)
Posted on 7/7/18 at 10:25 am
Posted on 7/7/18 at 10:25 am
This is on an 06 SLK280. Obviously blowing hot air. Compressor doesn't disengage, and the high and low side pressures are both at 140psi. All tubing is the same temp. It was last evacuated/vacuum tested/filled up by machine.
How would it just stick at 140psi on both sides? If the compressor is bad, shouldn't it be at the 55-ish that the low side was filled to? Obviously the high side is low, but the whole system is now equalized. I haven't ever seen that.
What gives?
How would it just stick at 140psi on both sides? If the compressor is bad, shouldn't it be at the 55-ish that the low side was filled to? Obviously the high side is low, but the whole system is now equalized. I haven't ever seen that.
What gives?
This post was edited on 7/10/18 at 10:04 am
8
Posted on 7/7/18 at 10:39 am to Hammertime
Do you hear the clutch kick in at all?
ETA: I really don’t know anything about the pressure of it.
My wife’s MDX was blowing hot air and it was the clutch relay went out.
ETA: I really don’t know anything about the pressure of it.
My wife’s MDX was blowing hot air and it was the clutch relay went out.
This post was edited on 7/7/18 at 10:40 am
Posted on 7/7/18 at 10:46 am to bbvdd
Fan speed alters inside the car, but I'm guessing that's a Benz thing. RPMs do not decrease, and clutch does not stop
Posted on 7/7/18 at 11:22 am to Hammertime
Prob a bad compressor, gauges are “closed” and reading same pressures?
Posted on 7/7/18 at 11:32 am to Redlos
What do you mean closed? They are screwed down, and the valves coming from the engine are open.
All I can figure is either stuck open expansion valve, or bad compressor. That's a huge difference in $$$
All I can figure is either stuck open expansion valve, or bad compressor. That's a huge difference in $$$
This post was edited on 7/7/18 at 11:34 am
Posted on 7/7/18 at 12:05 pm to Hammertime
It's probably the front sam (fuse box under the hood by the booster). It's what powers the compressor on that vehicle. Check and see if you have power at the compressor. If not, that's most likely the culprit
Posted on 7/7/18 at 12:13 pm to Hammertime
Make 100% certain the clutch is indeed engaged. Gauge dials closed . Equalized pressures of 140 under these conditions would indicate a bad compressor. The shaft of the compressor is broken or it's completely worn out. I want to know what the static pressure of the system is.?
Posted on 7/7/18 at 12:17 pm to windmill
these compressors are variable displacement compressors and dont have clutches like most mb in the last 15 years. 140psi on both side shows the compressor isnt working. also it could be 140 due to heat, pressure rises with heat, or it is over charged
Posted on 7/7/18 at 12:41 pm to ScottyB
I wondered if it was a VD unit or not. The diagnosis remains the same in this instance.Thanks for that clarification.
Posted on 7/7/18 at 1:04 pm to windmill
Not gonna be back to the house until later this afternoon, but will check static pressures later. The clutch is most definitely spinning, and the gauges are definitely closed off
Posted on 7/7/18 at 4:51 pm to Hammertime
The front of a VD compressor always spins with or without a/ c on. It's not a mg clutch setup. The compressor is run varying amounts by a solenoid in the compressor. Check pressure with engine off and then with engine running with ac turned on. If the pressure is the same I would want to make certain that the solenoid is getting the signal when a/c is turned on. Being able to read HVAC or PCM data would be beneficial. If it's not getting the signal then compressor failure is ruled out. If it is getting the signal and the pressures are still equal compressor is bad.
I don not replace just the solenoid in these systems. I put a new compressor with solenoid. I hope this helps you.
I don not replace just the solenoid in these systems. I put a new compressor with solenoid. I hope this helps you.
Posted on 7/7/18 at 5:02 pm to Hammertime
If the compressor is engaged and pumping then you have a bad compressor. That 140 sound like the saturated pressure at 90-95 degrees for 134A.
Posted on 7/7/18 at 5:49 pm to ScottyB
quote:
these compressors are variable displacement compressors and dont have clutches like most mb in the last 15 years. 140psi on both side shows the compressor isnt working. also it could be 140 due to heat, pressure rises with heat, or it is over charged
This compressor has a clutch. I bet it's the same factory Denso that's in the ML350.
Posted on 7/7/18 at 7:12 pm to Hammertime
Check to see if the compressor clutch is really not disengaging by unplugging the wires that lead to it while it is running.
Posted on 7/7/18 at 7:40 pm to Spankum
I'm gonna mess with it tomorrow. The nose of it definitely didn't stop spinning though. Still not back at the house, and I need to find a really skinny person to stick their arm down there 
Posted on 7/8/18 at 11:26 am to Hammertime
what you see is the clutch turning not the compressor, the compressor isnt running.
even a bad compressor would make the pressures have "some" change on each side.
and yes, when the compressor "is" running, it will have around 40-50 lbs pressure on the low side
even a bad compressor would make the pressures have "some" change on each side.
and yes, when the compressor "is" running, it will have around 40-50 lbs pressure on the low side
Posted on 7/10/18 at 10:03 am to Hammertime
7/10 Update:
I checked the static and running pressures. They are now the same for some reason. Both at 85/100. Ambient is around 90F. I guess that means the compressor is doing nothing, and it is possibly losing pressure, but how the frick did the low side get to 85psi, when it was only filled to 50?
My arm does not fit in the engine compartment, so I can't unplug the compressor to test electrical signal
I checked the static and running pressures. They are now the same for some reason. Both at 85/100. Ambient is around 90F. I guess that means the compressor is doing nothing, and it is possibly losing pressure, but how the frick did the low side get to 85psi, when it was only filled to 50?
My arm does not fit in the engine compartment, so I can't unplug the compressor to test electrical signal
This post was edited on 7/10/18 at 3:50 pm
Posted on 7/10/18 at 10:47 am to Hammertime
Plugged condenser or dryer can cause higher than normal low side pressure. So can low refrigerant, plugged or dirty air filter, expansion valve, and a few other things.
If you have lower than normal high side pressure and higher than normal low side pressure, your compressor is probably bad. I bet it fails a leak test.
If you have lower than normal high side pressure and higher than normal low side pressure, your compressor is probably bad. I bet it fails a leak test.
Posted on 7/16/18 at 4:08 pm to ScottyB
It's looking like the SAM unit is the culprit. Mechanic put the second new compressor in today. Said both his scanner, and one he went and borrowed both showed the compressor turning at 100% when it was called for, but hot air was still coming out. The compressor did have power going to it as per both scanners.
Now, it's gonna have to go to Mercedes for a $900 fuse box, and $125/hr labor on installing it and programming it to the car
Now, it's gonna have to go to Mercedes for a $900 fuse box, and $125/hr labor on installing it and programming it to the car
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