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So I recently noticed my A/C was blowing warm. I bought manifold gauges checked low pressure and high. Both pressures read the same 110psi in low and 110 psi on high temperature outside was roughly 80 degrees Fahrenheit. So I searched and things say it could be the heater valves or the compressor causing issues figured I’d see what the forums thought.
My low pressure is 110psi which is bad for low don’t you usually want 30psi
Unfortunately, your description is incomplete.
For example:
1 - Are those pressure values with the engine ON @1500 RPM, AC ON (lowest temperature setting) ? or
2 - Sitting pressures with engine and AC off for a while so the system can relax to the lowest pressure. For the latter, the ambient temperature becomes an important reference value because everyone expects the system to be at @Ambient temperature; therefore, you can expect a given pressure from refrigerant charts.
If your reported pressures are from (1):
1- you need to verify the clutch is engaged; otherwise, the compressor is doing nothing
2- if you have an MB-aware scanner you can verify how much is the computer is requesting from the compressor, i.e. actuating the electronic control valve. These are variable displacement compressors controlled by the AC module at will based on other sensors around the car (inside and out).
Monitor something like this (from @S-Prihadi 's recent post)
@juanmor40 with both the A/C off and vehicle off my and a ambient temp outside of 80 degrees Fahrenheit my low and high pressures are both around 80. With the vehicle on at idle and A/C on max setting ( the vehicle has been warmed up for 10-20mins) the low pressure is still around 80 psi and the high is also around 80psi. With RPMs at 2000 the pressures still do not change. I believe it’s the compressor but was unsure considering it is a different type of compressor so the clutch always spins I also checked the low and high pressure tubes going into the firewall both are the same temp and the heater valve also moves according when changing settings in the A/C. I have ordered a icarsoft mb v2 so that maybe I can read some diagnostics before replacing the compressor and other components just figured I could get more info here. Thoughts @juanmor40
Does your AC control panel have a digital display?
You need to check if there is voltage at the back of the compressor. For 2008, here are the compressors -> same for RWD and 4Matic
Can you see the yellow dot at the back? That is the Electronic Control Valve (with a DIode), you need to measure if there is power at the connector just on top. Either back probe, or disconnect and measure on the incoming wire.
What would I need to be able to measure if that’s working or not? @juanmor40 any links to the tool specifically? I haven’t gotten under the vehicle yet. Maybe we could pm on the topic
@juanmor40 with both the A/C off and vehicle off my and a ambient temp outside of 80 degrees Fahrenheit my low and high pressures are both around 80. With the vehicle on at idle and A/C on max setting ( the vehicle has been warmed up for 10-20mins) the low pressure is still around 80 psi and the high is also around 80psi. With RPMs at 2000 the pressures still do not change. I believe it’s the compressor but was unsure considering it is a different type of compressor so the clutch always spins I also checked the low and high pressure tubes going into the firewall both are the same temp and the heater valve also moves according when changing settings in the A/C. I have ordered a icarsoft mb v2 so that maybe I can read some diagnostics before replacing the compressor and other components just figured I could get more info here. Thoughts @juanmor40
If the iCarsoft v2 is not a bi-directional scanner, I would return if possible. You want a Bidirectional MB-aware scanner, either iCarsoft v3, or Creader Launch 431 v2 for Benz, or an XEntry clone, but if you plan to keep the car for long, you WANT a bi-directional scanner.
What would I need to be able to measure if that’s working or not? @juanmor40 any links to the tool specifically? I haven’t gotten under the vehicle yet. Maybe we could pm on the topic
Here is a video explaining how the ECV works "generically" to understand the basics.
You can diagnose w/o using the higher-end tools shown there. For example,
0 - CHECK the AC fuses are all good. (https://fuse-box.info/mercedes-benz/...uses-and-relay )
1 - with the scanner you can activate the ECV manually, and see if the compressor reacts.
2 - You can measure voltages on the connector at the top of the AC compressor.
3 - You can also measure the resistance of the ECV to check if not shorted, or open (blown).
First, understand the basics, then measure data to see what is off, analyze, and plan the next step. There are no magic bullets here.
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