S320 AC problems
 

On my 95 S320, the AC compressor does not engage. I can turn both sides of the CCU to Lo, and still nothing. As far as I know, when I do that, the clutch should engage at any temp. Today when I looked at it, it was 8 degrees C outside.
I dont' know if this is related, but the instrument cluster isn't showing outside temp all the time. Happens intermittently.

Got 2 codes from the CCU when I checked. E045 and E075.
Is it possible that my R134a is just low, and that caused my E045 code?? How can I check the pressure if the clutch won't engage?? If I hook my AC gauges to it, which side does each line go to?? I have red, blue, and yellow lines. Yellow, I believe goes to the bottle I'm filling from, iirc....

bump

Where did you get those codes from? They don't look right. A/C codes are usualy in the form of Eb1 xxx. Use the procedure here to get the A/C codes and post what you find.

That link is for the E class W210. His is different (but similar). Those codes are right for his car.

Current sensor values: Set temperature wheels to white area. Igniton ON. Press left and right AUTO button. Wait at least 20 seconds then press REST for >5 seconds.

Scroll with left AUTO button to read current-sensor values. Write these down.

E045 is "refrigerant pressure sensor (B12), short circuit"
E075 is "Coolant circulation pump (A31m1), open or short circuit"

Yep. I had looked up the codes. The E075 has been around for a long time, but I still get proper heat. That doesn't seem to be a problem, although I might look at replacing the aux pump sometime soon here.
The AC pressure sensor is my concern right now. Could it just be that my pressure is low. When I looked through the code list, I didn't see a code for low refrigerant pressure. If the pressure is low, it's an easy fix, where as opening the system is a much harder fix.
I also don't have much of the equipment mentioned in the WIS to test, so I was wondering about homebrew testing....

I didn't look through the whole list of codes; I just looked for those that you mentioned.

Measuring the static refrigerant pressure is the next step. You'll want to use the blue hose, since it goes to the low pressure gauge. With the car stone-cold, connect it to the low-side fitting and read the pressure, and translate that to refrigerant temperature (this may be marked on your dial). It should read ambient. It will read lower if you are essentially out of refrigerant (no liquid left in the system) but could charge it. If it reads 0, you should replace the dryer as a minimum (after fixing the leak).

With the leaky evaporators known to be an issue on these cars (especially on the earlier models) checking refrigerant pressure is where I would start. A leaking evaporator will slowly exhaust the entire system of refrigerant and the low pressure shutoff switch will stop the compressor from self destructing. Did you notice a slowly creeping bad performance in the system before the compressor would no longer engage?

Evaporator replacement on these cars is a bit on the expensive side as it requires the complete removal of the dash which is labor intensive. I have read about some owners using "leak stop" additives to prolong the replacement with varying degrees of success and failure.

In most of the time that I have owned this car, I have not used the A/C that much. It worked last summer the 3 times I can remember using it. It's been fairly cold around here lately. It woudl be getting close to a year ago that I last used it. It could have leaked down, and I just didn't notice.....
Another possible problem or symptom I noticed while my sister was driving the car today was that I didn't seem to be getting any major amounts of heat on the passenger side. The drivers side was set a few degrees cooler, and was much hotter. The passenger side was only blowing moderately warm air.
Duovalve perhaps?? Or the aux pump??

bump

again, bump....

Do you have pressure in the system?

Ac or coolant system?? Haven't had time to check either. Hopefully tomorrow morning.
Grabbed another duovalve out of the wrecked S420. Hopefully one side is good in it, and I can swap it into the one I have.

As I understand it, it's a common occurrance to get a 075 error on these cars. I replaced my duo-valve at a considerable expense to try to get rid of the code, and got the code back within a few days of the installation. I've been told on more than one occasion "don't worry about it as long as your heat works correctly."

If you've got unbalanced heat, the duo-valve is where I'd start.

To confirm, you can also check under the hood while the car is at operating temp - there are two hoses coming from the heater core (engine coolant flows into the core in a single pipe and exits to the duo-valve through two pipes). Having an infrared thermometer helps, but you can test it with your hand if you're careful. The pipes run along the bulkhead to the right of the throttle actuator. They're about 1/2" (26cm) in diameter. See if one is noticeably different in temp than the other. If so, either the duo-valve is malfunctioning and not allowing the coolant to flow out of that side of the heater core, or you've got a blockage.

Pulling sensor values will also help. Dials to white - CC on. Press and hold Rest for 5+ seconds. Cycle through the codes with the left Auto button. Register 3 is the left heater core temp, register 4 is the right heater core temp. If the temps say the same, then likely the sensor for the right core (if the right side is the one that's cooler in the car) is defective and the CC thinks the temp is right.

to run the sensor values, do I ahve to have the car running, or shut off with the key in the on position?? I'm assuming it needs to be running....

I checked out the heat. from cold, sensor 3 and 4 were saying +/- degree of what my infrared thermometer said the temp in the car said it was.
After I warmed the car up with the heaters on max, register 3 said it was about 70C, and the passenger side was saying 35-37.
I checked the hoses off the duovalve. the bottom outside (side closest to the fender) hose and the center hose were about 35C, and the bottom inside hose, and the top hose were 70-80C. I'm thinking the duovlave is at fault. I picked up a second one from the junkyard. I figure if I take that apart, and take a good side from it, my heat should work again.
Haven't checked the A/C pressure yet. The low pressure fitting is in the front, right next to the ac cooler, isn't it??