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2002 C320 AirCon with 170,000 miles blows warm. It just stopped working. I noticed a slight burning smell in the cabin when I stopped at a light. (I was opening the passenger door that day and when leaning over I tripped the little SDS door and banged it pretty good with my head. I know there is a sensor in the overhead panel and wonder if I disturbed it enough to shut down the AirCon, unlikely, I think.)
I have the Star CD (using for the first time and trying to make sense of it), plus I have read many threads on the subject, but don't know where to start troubleshooting the problem.
A month ago I started to hear the "clicking" in the dash. It would go away after 10 seconds or so. I pressed the recirculate/defrost buttons and the LED lights alternated but never stopped. I haven't been able to get climate control codes. I read a high (danger 65psi) pressure on the high side port.
My intention is to hook-up gages on the high and low side, add 134a and use my detector to search for leaks. I also want to troubleshoot sensors and the pressure switch.
Can anybody help me testing the pressure switch (or where on the CD it tells me how to do it)?
Have you ever replaced the alternator?
The burning smell might be from the belt slipping (over time, the alternator overrun pulley seizes and it tends to break the AC compressor pulley in turn). Any vibration/chirping noise with the AC on recently?
High side pressure should be on the order of a couple hundred psi when the AC is on.
I'd do as you are planning to - hook up the gauges, check the static pressure; turn on AC, check dynamic pressures.
If static pressure is OK (i.e. no leaks) then proceed with sensors etc.
But I'm suspicious of the burning smell you have mentioned... Believe it's possible to jump the compressor directly from the battery and see if it actually works. Or maybe check that the car supplies the voltage to the compressor when you turn AC on?
UPD: See this post: https://mbworld.org/forums/c-class-w...ml#post5730107 You definitely can engage the compressor by applying 12v to it. Just pay attention and don't run it like that for long time. (E.g. if the freon is low you may fry the compressor)
Let's go back to the clicking in the dash. That usually means broken actuators on the step motors that position the flaps in the air handler. The C class has no hot water valve, and the flaps move to send the hot air outside when air con is desired. You might have full reheat. The clicking stops after a few attempts as the controller gives up. It is a big job to change the actuators, but it has to be done to have full functionally.
The C320 does not have an alternator over run pulley. That is a four cylinder invention. There is also no electrical connection on the compressor. The compressor is driven all the time.
The system pressure switch can be checked electrically. Run the air con a few minutes. Turn off the car, and measure the continuity of the switch. If it is shorted the switch is good.
For the vast majority of people the tools to properly address Air Con problems are just too expensive. You will be money ahead to allow a pro to turn the wrenches.
Hey Moviela, how is the compressor swash plate angle changed if there is no electrical connection to it?
The plate is moved by a proportional control circuit external to the compressor. It is not a binary off/on device. Connecting to battery voltage might destroy the controller.
Perhaps I should have been more clear (I was typing on my phone) that there is no connection to the compressor clutch. It does not have a magnetic clutch like in days of yore.
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
The full HVAC operation is in the Wiki. This is 99% sure a broken stepper motor arm on the Blender flap as Movie says. Part redesigned after 2002. 320 has the most stepper motors of all W203 models.
Thank-you for replies. The clicking occured for a month or so and the a/c was fine until it started blowing warm last week. I have not noticed a change in the click sound. I suppose the blender flap must be in the correct position for the a/c to operate?
I did notice a wining sound under the hood but it stopped after a short while. Low side reads 75psi with engine (a/c) on and off. (I couldn't get the high side to accept the gauge hose.)
If the compressor runs all the time, I will try to check the pressure switch before I attack the blender flap. Are there DIYs for checking the switch and fixing the flap?
Moviela, ah, ok... I thought it might be some sort of PWM control signal, so thought one could just jump it directly (kind of simulating the "full strength" operation with a 100% duty cycle). But that might not be a good idea if the control is actually more involved. (but people have done it, e.g. here: https://mbworld.org/forums/c-class-w...ml#post5730107)
C230 & Glyn, he'd actually done that in the first post
Benzbit, looks like the compressor is not engaging - you would see the low-side pressure drop and fluctuate with the AC on and working.
75psi sounds like a normal "off" pressure for 70F ambient temp.
1. Not sure about this, but it's supposed to turn on when the AC is on, but I guess these cars have some smart sensors to not turn on the fan if the compressor is not engaging.
Does the fan work when the car is hot though?
2. When not in "auto" mode, they should just route the air through the evaporator, as you can see in Glyn's picture.
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
I think you need to accept that there is possibly more than one thing wrong here. The clicking is indicative of stepper motor/arm problems.
The compressor might be toast but a competent HVAC shop needs to diagnose this. When you angle the swash plate & start stroking the pistons does the compressor start pumping/compressing the refrigerant or not?
The compressor, dryer and fan have been replaced and charged. The A/C does not operate. Can anyone direct me how to reprogram the climate control system?
08-24-2014, 01:20 PM
