A/C diagnostic mode values for pressure?
Thread Starter
Senior Member
Joined: Feb 2017
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From: Australia
W202 C43 1999
A/C diagnostic mode values for pressure?
Hi all,
What sort of values should i expect to see on #7 when in diagnostic mode?
While sitting at idle for a couple minutes i see around 26°5ish, and while driving on the highway it was down around 7°2ish and a bit lower.
I would have to assume this value is in kPa.
Thanks all
What sort of values should i expect to see on #7 when in diagnostic mode?
While sitting at idle for a couple minutes i see around 26°5ish, and while driving on the highway it was down around 7°2ish and a bit lower.
I would have to assume this value is in kPa.
Thanks all
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From: America
1999 C43 AMG, 2005 E55 Wagon
If the AC is running, the pressure will fluctuate. The compressor will build up pressure and release it. That's how it cools. Ever used one of those air horn cans? It's under high pressure. As you press the horn button, it releases pressure and causes it to become very cold in your hand. The colder it gets, the less it performs. And obviously the lower the pressure the less cold it can achieve.
An AC system is just a way to recycle that stuff back into the can to build up pressure to a certain point so that it can release and cycle back around and repeat.
With engine running and AC on, you should see that number fluctuate slowly between 2 different points. 26.5bar seems awfully high, but I can't remember the spec.
An AC system is just a way to recycle that stuff back into the can to build up pressure to a certain point so that it can release and cycle back around and repeat.
With engine running and AC on, you should see that number fluctuate slowly between 2 different points. 26.5bar seems awfully high, but I can't remember the spec.
Thread Starter
Senior Member
Joined: Feb 2017
Posts: 392
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From: Australia
W202 C43 1999
Yes i know how A/C works, i am an electrical fitter/mechanic by trade and spent over 17 years in the game, but looking to see what values should be expected on this set up 
It is certainly not giving a reading in bar, if it is metric, which id say it is, the reading will be kPa.
26.5 bar is almost 385 psi, and you will never see that on the low side. 265kPa is 38ish psi.
It is certainly not giving a reading in bar, if it is metric, which id say it is, the reading will be kPa.
26.5 bar is almost 385 psi, and you will never see that on the low side. 265kPa is 38ish psi.
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From: America
1999 C43 AMG, 2005 E55 Wagon
ok, great. I just try to be blunt, when I started trying to figure out my AC woes I had to learn how the system worked (and a LOT of people have no idea how they work, they just ask "why isn't it working???").
so, sorry if that came across wrong.
I had no idea they measured in kPa over there, since they measure in bar here (but nothing else here is measured in bar, so I thought it was just what MB did world-wide)
But if it IS measuring in bar, then would that mean the pressure sensor is faulty? yeah, 385 would pop the evaporator in a heartbeat.
if it has the little "o" between the 26 and the 5, then its trying to say 26.5, if there's no little "o" it is trying to tell you 265, so maybe that's helpful?
so, sorry if that came across wrong.
I had no idea they measured in kPa over there, since they measure in bar here (but nothing else here is measured in bar, so I thought it was just what MB did world-wide)
But if it IS measuring in bar, then would that mean the pressure sensor is faulty? yeah, 385 would pop the evaporator in a heartbeat.
if it has the little "o" between the 26 and the 5, then its trying to say 26.5, if there's no little "o" it is trying to tell you 265, so maybe that's helpful?
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From: Henrico, Virginia
2014 ML350 4Matic
26 is way too high for compressor discharge (high side) pressure. I seems like you are not getting enough air flow through the condenser when at a stop. Typically what I expect to see is 6-8 when moving and a steady rise to 14-17 at a stop on a warm day.
This can count as a response to your question about the aux fans - they should be running at a stop when your high side pressure is this high. The pressure switch on the receiver/filter should be calling for the fans to run in your case.
This can count as a response to your question about the aux fans - they should be running at a stop when your high side pressure is this high. The pressure switch on the receiver/filter should be calling for the fans to run in your case.
Thread Starter
Senior Member
Joined: Feb 2017
Posts: 392
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From: Australia
W202 C43 1999
26 is way too high for compressor discharge (high side) pressure. I seems like you are not getting enough air flow through the condenser when at a stop. Typically what I expect to see is 6-8 when moving and a steady rise to 14-17 at a stop on a warm day.
This can count as a response to your question about the aux fans - they should be running at a stop when your high side pressure is this high. The pressure switch on the receiver/filter should be calling for the fans to run in your case.
This can count as a response to your question about the aux fans - they should be running at a stop when your high side pressure is this high. The pressure switch on the receiver/filter should be calling for the fans to run in your case.
Should the receiver/dryer be hot or cold during operation? On Corvettes it would get ice cold, but the whole setup is different to this car.
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Super Member
Joined: Nov 2001
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From: Henrico, Virginia
2014 ML350 4Matic
#7 is refrigerant pressure in BAR, so high side.
I don't have cut in pressures for the later cars handy at this time. The early cars (with the dual aux fans like the C43) have two relays mounted in the relay/fuse box in the engine compartment (K9/1 and K10). The relays have a fuse on top. If your car is similarly equipped check the fuses.
These following values for the older cars but I think yours is similar.
The aux fan switch points for refrigerant pressure are (in BAR) = 1st stage 16 on, 13 off. 2nd stage 20 on, 17 off.
The switch points for engine temp (ECT sensor (B10/8) are (in degC) = 1st stage 100 on, 95 off. 2nd stage 115 on, 107 off.
In case you don't know, the fans have two stages - high and low.
The receiver is on the liquid side of the system (high side). It will be warm. I don't know about Corvettes. Placing the receiver on the low side serves no purpose so I don't know why anyone would do that.
I don't have cut in pressures for the later cars handy at this time. The early cars (with the dual aux fans like the C43) have two relays mounted in the relay/fuse box in the engine compartment (K9/1 and K10). The relays have a fuse on top. If your car is similarly equipped check the fuses.
These following values for the older cars but I think yours is similar.
The aux fan switch points for refrigerant pressure are (in BAR) = 1st stage 16 on, 13 off. 2nd stage 20 on, 17 off.
The switch points for engine temp (ECT sensor (B10/8) are (in degC) = 1st stage 100 on, 95 off. 2nd stage 115 on, 107 off.
In case you don't know, the fans have two stages - high and low.
The receiver is on the liquid side of the system (high side). It will be warm. I don't know about Corvettes. Placing the receiver on the low side serves no purpose so I don't know why anyone would do that.
Super Member
Joined: Nov 2001
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From: Henrico, Virginia
2014 ML350 4Matic
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12' W204 C63 AMG coupe "T-Rex", 12' W451 Smart Fortwo Pulse (99' W202 C43 AMG + Ultima Can-Am sold)
MBWorld Fanatic!
Joined: Mar 2010
Posts: 5,889
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From: Land of mountains, cheese, chocolate and watches
12' W204 C63 AMG coupe "T-Rex", 12' W451 Smart Fortwo Pulse (99' W202 C43 AMG + Ultima Can-Am sold)
