A/C Compressor Doesn't Always Click On - Page 2 - PeachParts Mercedes-Benz Forum

ah-kay · #16 05-29-2009, 01:49 PM

Try this for intermittent problem on MBZ.

http://www.continentalimports.com/ser_ic60046.html

BTW: compressor is cycled on/off by the control unit, depending on temp, engine load, engine temp etc to protect the engine. Why would the ACC controls the coolant through the heater core? Like you turn on the heater when the A/C is too cold?

leathermang · #17 05-29-2009, 03:38 PM

Quote:

Originally Posted by tangofox007

As I understand the operation of the ACC, the temp is regulated by varying the flow of coolant through the heater core, not by cycling the compressor off and on. It is my belief that the compressor should run continuously except in the EC and OFF modes, where it does not run at all. In other words, if the normal, bi-level or defrost modes are selected, the compressor should be engaged regardless of the temp selection.

Perhaps you are thinking of a later style ACC system... I am pretty sure his is still a cycling clutch type... the primary control being the ' operator controlled variable temperature ' on the dash...
A later style...with an accumulator and orifice would typically have the compressor on all the time...

Matt L · #18 05-29-2009, 07:29 PM

CCOT doesn't mean later. It usually means American, although the system is used in other cars.

TXV systems typically lack low-side cutout switches and thus cannot cycle based on the pressure. Instead, they cycle only on evaporator temperature. If the evaporator drops below about 3C, the compressor stops. It will start very shortly as the temperature will increase pretty much right away.

My 210 has a variable-displacement compressor (the '82 would not have one of these) which regulates the low-side pressure. This makes it so the evaporator will not freeze under normal operation. Of course, there is still an evaporator temperature sender. There is always one of those. But unless I specifically shut it off (with the EC button), the compressor runs if it is >3C ambient temperature. The heater cores are the only elements used to regulate the cabin temperature.

tangofox007 · #19 05-29-2009, 09:14 PM

Quote:

Originally Posted by leathermang

Perhaps you are thinking of a later style ACC system...

My comments were based on the assumption that the subject vehicle was equipped with the same ACC system as other '82 W123's. After looking into it, I find that some sources say that it is, while others reference a different system. So, if the subject vehicle is not ACC equipped, my comments in this thread should be disregarded.

mjquillici · #20 06-01-2009, 07:49 PM

Quote:

Originally Posted by tangofox007

I have a question, too. Does the compressor ever disengage while the a/c is operating? For example, the a/c is operating normally for 10-15 minutes and then just starts blowing warm air? Or does the compressor only fail to engage after the a/c has been turned off?

I have been out of town for the last couple of days and came home to a whole bunch of responses. Thank you!

To answer the question above, once the A/C compressor clicks on initially, it continues to cycle on and off normally. I haven't decided yet if the temperature of the cold air seems to be fluctuating more than usual.

If the A/C compressor DOES cycle on and off normally after it has been turned on initially, would this indicate that it is more likely a relay issue and not the regulator?

As of right now, I'm thinking that I may try replacing the relay first, and if that doesn't fix the problem, then proceed to replacing the regulator. What do you all think?

EDIT: I just did some research about how much the relay costs, so now I'm thinking that I may replace that as a last resort. . .

leathermang · #21 06-01-2009, 09:17 PM

A good little pencil thermometer which can be stuck into the vent AND LEFT THERE will give you a lot of facts to deal with instead of ' feelings' which are affected by things like what you are wearing, whether your wife is yelling at you and the relative humidity.
They only cost about $6.

leathermang · #22 06-01-2009, 09:22 PM

What does the temperature setting device in your car look like? Is it the vertical partly hidden wheel ? Some of these symptoms also sound like they could be caused by your pushbuttons on the dash...you have those correct ?

Matt L · #23 06-01-2009, 09:36 PM

Quote:

Originally Posted by leathermang

A good little pencil thermometer which can be stuck into the vent AND LEFT THERE will give you a lot of facts to deal with instead of ' feelings' which are affected by things like what you are wearing, whether your wife is yelling at you and the relative humidity.
They only cost about $6.

+1 on the vent thermometer. My Benz has one. I got it from the grocery store on the cookware aisle, but all sorts of places sell pencil thermometers.

mjquillici · #24 06-01-2009, 11:39 PM

Quote:

Originally Posted by leathermang

What does the temperature setting device in your car look like? Is it the vertical partly hidden wheel ? Some of these symptoms also sound like they could be caused by your pushbuttons on the dash...you have those correct ?

Thanks for the pencil thermometer idea. I should have thought of that. I will pick one up.

Quote:

Originally Posted by leathermang

What does the temperature setting device in your car look like? Is it the vertical partly hidden wheel ? Some of these symptoms also sound like they could be caused by your pushbuttons on the dash...you have those correct ?

The temperature setting device is the partially hidden vertical wheel. I have the analog controls, not the push button controls.