Automotive Air Conditioning Information Forum

JohnHere wrote: ↑Mon Jun 24, 2024 8:01 am Can you get at the TXV without disassembling the dash? If so, then the job will be much easier.

Luckily yes I can, it's just under the wiper cowl at the firewall.

JohnHere wrote: ↑Mon Jun 24, 2024 8:01 am You can replace only the control valve, but not without first recovering the refrigerant to attain zero system pressure. If you have to remove the compressor anyway to gain access to the CV, you might as well replace the entire compressor given it's age and the mileage factor.

I agree. There's a possibility it's gummed up or something. I'll see if I can just remove it to look at it after I recover the refrigerant. May be accessible without removing compressor.

Also pay attention to the appearance of the oil. It should be light amber in color. If it's dark brown or black, possibly with particles in it, then we have additional problems.

Well holding it at 1500-2000 rpm definitely paints a different picture of the system. Low side was going to 25 and high side was at 225. Certainly a low charge right? I added some more refrigerant and got the low side to 30 or 32 and it is actually cooling better, but this system has a problem at idle (where I need the cooling the most since I just sit in the car sometimes for lunchtime at work) Idle pressures are 45/188.

Most ac issues on 2000’s Mercedes are caused by the “duovalve”, more specifically a coolant valve that blends heater core air with specific climate zones within the car. If you have one cold vent, and others are warm, it’s almost always the coolant valve

As John stated, an auto AC compressor does almost no work at all at idle, it is not possible to make it do otherwise. The only answer to your cooling needs at lunch is to rev the engine to 1500 or eat inside somewhere

Ctravis595 wrote: ↑Thu Jul 04, 2024 8:46 pm Most ac issues on 2000’s Mercedes are caused by the “duovalve”, more specifically a coolant valve that blends heater core air with specific climate zones within the car. If you have one cold vent, and others are warm, it’s almost always the coolant valve

I'm aware of the duovalve issues and I've ruled that out. It properly is circulating coolant through the heater core. The scan tool shows the two 'heat exchanger' temperatures and they are close to what the evaporator temperatures show on the scan tool. Evap is about 3-4F cooler.

I managed to replace the a/c compressor (purchased a Denso unit) and replacing it was an unbelievable pain. I recharged the system to 34oz after vacuuming and I am getting higher high side pressures now (45/200) at idle (93F ambient) but cooling performance still sucks. Getting 60F vent temps at idle after car was driven for 10 minutes. There is an enormous temp difference while driving and while idling. Gets 10F warmer at idle. The cooling fan spins but it does not spin 100% at idle. It spins harder only when I give it higher RPM's at idle. Not sure if this is normal or not. I'm not sure if I posted here earlier but I also did change expansive valve (new oem) with not much difference.

The one thing I think I screwed up on is I didn't change out the drier. I have a feeling that it may be the problem now and I've ordered one and will replace it.
I also feel that charging to weight is B.S. because when I'm at 2000 rpm at idle, my pressures go to 20-25 low and 215-220 high. It feels like I'm still undercharged. I should charge it by the pressures?

Your 7:59 post confuses me. Are we certain that there is no re-heating of the AC air? I would clamp off a heater hose to see if there is any difference.
I would also get after that fan. The comp does little work at idle as mentioned, so having all the fan possible will be important at idle.
Finally yes the R/D should have been changed.
As to any additional charge, I will leave that for John to comment. But your high side is about where it should be. What was the ambient for your last set of readings? Always give ambient when you give pressures.

tbirdtbird wrote: ↑Mon Jul 29, 2024 6:48 am Your 7:59 post confuses me. Are we certain that there is no re-heating of the AC air? I would clamp off a heater hose to see if there is any difference.
I would also get after that fan. The comp does little work at idle as mentioned, so having all the fan possible will be important at idle.
Finally yes the R/D should have been changed.
As to any additional charge, I will leave that for John to comment. But your high side is about where it should be. What was the ambient for your last set of readings? Always give ambient when you give pressures.

I'm certain the coolant circulation pump is not an issue because it doesn't run when the climate controls are set to maximum cooling. The scan tool also shows the duovalve duty cycle and it is not activated, so essentially coolant isn't circulating through the heater core when the valve is off. In my previous post I meant that the valve is working when I demand heating at the climate controls.

Also, the 20-25/215-220 was taken at 95F, car standing still, 2k engine rpm, max cooling, windows open. We tend to have the same exact weather here in FL every day in summer. Sunny, 90-93F, 60 percent humidity.

Ok, changed out the drier, evacuated system for an hour, recharged on the liquid side to exactly 34 ounces with my refrigerant recovery machine. Didn't even have to turn on the engine. Awesome right? I think we're back in business. I think I was undercharged before, I pulled 26.6 oz out. I'm getting the hang of this. I may have done some bad math before with my scale. Car is cooling very nicely now, pressures are 35/215 at 85F @ 1500rpm. I mean it was 85F and at night, went for a drive, and saw the evaporator temps at 38F. Never even seen that before on this car. I know it will cool a bit less when sitting on the sun but I think this is as good as it gets. Thanks all for the help.