Is A/C compressor DC voltage or PWM activated?
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From: San Jose, CA
01 CLK430
Is A/C compressor DC voltage or PWM activated?
01 CLK 430
I am suffering from a lack of A/C which doesnt seem to be a rarity for mb owners. I have already read all of the threads and dont believe my question has been answered. The A/C has not worked since I bought the car so I dont know what was or wasnt done before that. Hopefully it isnt plugged by some stop leak stuff.
So, here is what I know. The compressor clutch never engages. If I go into diagnostics, all of the sensor values look good. There appears to be plenty of cryogen in the system. I topped it off with a UV dye and I cant find any leaks. If I go into the stored errors, I get a whole handful. I dont have them in front of me, but there were a whole bunch. I disconnected the signal ot the compressor and measured it with a DVM. Again, it was disconnected, not spliced into so that may not be the best way to test the signal? Anyway, with a dvm and the climate control off, I get approx 9.30 volts. If I turn the climate control on, the voltage goes up incrementally to a maximum of 9.60 vlts when on high. I didnt break out the oscilloscope to check, but I wondered if the compressor is engaged via a pulse width modulated 12 volt signal, or if it really is just a DC signal. The next obvious question is: what is the correct expecation?
I can definitely make a guess, but I am looking for a definitive answer from a tech, from a manual, or someone who has diagnosed the system like this.
Thanks in advance for any insight.
Chris
I am suffering from a lack of A/C which doesnt seem to be a rarity for mb owners. I have already read all of the threads and dont believe my question has been answered. The A/C has not worked since I bought the car so I dont know what was or wasnt done before that. Hopefully it isnt plugged by some stop leak stuff.
So, here is what I know. The compressor clutch never engages. If I go into diagnostics, all of the sensor values look good. There appears to be plenty of cryogen in the system. I topped it off with a UV dye and I cant find any leaks. If I go into the stored errors, I get a whole handful. I dont have them in front of me, but there were a whole bunch. I disconnected the signal ot the compressor and measured it with a DVM. Again, it was disconnected, not spliced into so that may not be the best way to test the signal? Anyway, with a dvm and the climate control off, I get approx 9.30 volts. If I turn the climate control on, the voltage goes up incrementally to a maximum of 9.60 vlts when on high. I didnt break out the oscilloscope to check, but I wondered if the compressor is engaged via a pulse width modulated 12 volt signal, or if it really is just a DC signal. The next obvious question is: what is the correct expecation?
I can definitely make a guess, but I am looking for a definitive answer from a tech, from a manual, or someone who has diagnosed the system like this.
Thanks in advance for any insight.
Chris
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Joined: Jan 2005
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From: Orange County
2005 C Wagon (No snickering please!)
The wiring diagram shows a simple clutch, so DC would be expected. One end of the clutch is connected to chassis, and the other end goes into a black box called AAC. I would think there would be a transistor in there to turn on the clutch, and expect a slight voltage drop of less than a volt through the AAC.
I am not sure which compressor is in your car. There are some that have a variable displacement compressor. A rod controlled by a PWM signal adjusts the angle of the swash plate in the compressor. Sometimes these will buzz when the control system can't figure if it wants a big or little compressor.
I am not sure which compressor is in your car. There are some that have a variable displacement compressor. A rod controlled by a PWM signal adjusts the angle of the swash plate in the compressor. Sometimes these will buzz when the control system can't figure if it wants a big or little compressor.
