amstel78

Just realized this afternoon that the rear climate control A/C doesn't appear to be functioning. Control panel works along with blower, but air coming out is warm. A/C up front works fine and the air is ice cold.

If memory serves, the M275 has a second compressor and separate circuit for the rear. I'm wondering if it needs a refill of R134. Can anyone please let me know where the A/C schrader valve for the rear is located?

I'm going to do a bit more googling and research, but if I'm also just missing the obvious, I'm all ears.

Edit: I'm mistaken about that 2nd compressor. Don't know why I thought that. Maybe it was the Maybach engine I was thinking of.

amstel78

Doing some research, some have suggested replacing the duovalve which services the rear vents. The part number is 2208300284 and this duovalve is located by the right front wheel arch. Does this sound like the culprit for cold A/C up front, and warm air out back?

https://www.fcpeuro.com/products/mer...mer-2208300284

DrDoe

Warm air for all settings even LO?

amstel78

I didn't try the lowest setting in the back so I don't know. I'll give it try later. If it starts to cool, then what? Still the duovalve?

Fwiw, the air coming out isn't hot. It's not exactly cold either. There were moments when it felt like it was coming down, but then returned back to the warm side again. The front vents however put out cold air so I don't think it's refrigerant.

DrDoe

The sensor in the back could be broken if cold air with low setting

amstel78

Can't seem to locate that sensor's location in Google. Can you please elaborate on where that sensor is?

Found this on Youtube:

I assume there's two of these sensors? One for front and one for rear? If there's only one sensor, then it's working fine as I don't have any issues with the auto climate control up front.

DrDoe

So it blows cold air with LO setting? I assumed there is a sensor. I haven't looked for one.
You might want to check the diagnosis for rear AC first before throwing a $400 part at the problem

amstel78

Well, I just got back from fiddling some more with the rear climate control. This is what I've discovered:

1. There's not much of a difference when setting temps from 68F to LO in terms of coolness. Outside air temps are presently 82F.

2. Bringing the temps back up from LO to 68F doesn't increase air temps;

3. Increasing one side.. in this case, the right rear passenger temp settings to a higher temperature of 78F does bring the air temperature of that side up accordingly. I kept the left side at 68F and there's a noticeable difference.

4. Reducing the right side temperature to match that of the left side does bring the temps back down but it does so quite slowly.

All of the above leads me to believe that the rear climate duovalve that's located in the front passenger wheel arch is functioning. However, the air coming to the rear just isn't as cold as the front. Additionally, the front air temps while cold (and I did say ice cold before but now that's probably an exaggeration), are really not that cold. They're comfortable and will cool the vehicle down on a hot day, but it's not arctic cold like a system running at its peak.

I will try an R134 recharge first. Hopefully the system is just a little low on refrigerant.

Quick question. The low pressure side for refilling is the one on the left in the picture below? It's also cold to the touch whereas the right side is warm. Usually the low and high pressure ports are differentiated by color coded caps, but in my car, both caps are black.

DrDoe

The larger diameter line is low pressure and the smaller diameter line is high pressure. Sounds like you are going to get the cheap $30 part for refill. Good luck with that.
Once advice I can give you is to make sure you select the pure R134a can and not some cans with other junk added.

amstel78

What about the stuff with oil combined like this?


The last time I used one of these cheap kits was to convert and revive an A/C system in a W123 years back. It worked well.

DrDoe

It said with system leak sealer right?
Stay away from them.
Both under filled and over filled will degrade your system and you don't know how much to add. MB is offering $100 off for >$200 service until 5-31-17. You might want to consider that route for the AC system.

DrDoe

Here is the link to get $100 coupon: Spring
My last AC service at the dealer was $155 so it's not quite at the $200 minimum but the rate at bigger cities might be higher. Perhaps you can add 30min diagnostic service...

E42AMG???

You can buy a gauge and line set for 60 dollars, a scale to weigh how much you put in is like 20 dollars, or a home scale that goes to tenths of a pound. Then buy a tank they sell 5-30lb ones for 30-100 dollars. Don't put anything with additives in the system.

amstel78

I bought a set of gauges; high and low pressure, and three 12oz cans of DuPont R134A refrigerant (no oil or additives). Total cost: $60.00

I will compensate for ambient temps while refilling the system. Shouldn't take long. Hopefully that solves my problem.

DrDoe

Get a thermometer, a meat thermometer would work. Stick the thermometer in the vents of all 4 zones. Set fan speed to minimum and temp to LO. Record the temperature for all 4 zones before and after. The temperature readings should be in the low 40s.

E42AMG???

Curious about your issue I checked mine today and the passenger side is blowing hot air

amstel78

That sucks. Front vents or rear?

E42AMG???

Rear

amstel78

What about the rear vents in the B pillar? Are those warm or cold as well? In my case, the air coming out of those are cold.

Try the little experiment I detailed a few posts up. If you get a similar result, then the duovalve located in the front passenger wheel arch might still be OK and your car just needs refrigerant. Let me know how it turns out.

wallyp

With the AC on max cool, feel of the larger refrigeration line on the left front fender - it should be cold enough to have dew (condensed moisture) on the line, but not frost. If it is cold, the refrigerant level isn't too bad. If it is warm, the level is low or there is another problem in the system. If the line is frosted (not common on the W220), the level is a little low.

amstel78

I'm going to check with manifold gauges.

E42AMG???

The pillar vents get air from the front. I have 12 bar at idle and 9 ish when cruising so it has enough refrigerant, so there is a seperate duovalve then the one under windshield cowl?

amstel78

Yes. The second one under the passenger front wheel arch cover handles the rear climate control vents coming from the center console.

Check out this thread, in particular post #6:
http://www.benzworld.org/forums/w220...g-problem.html

I believe this is the part# for the duovalve: https://www.fcpeuro.com/products/mer...mer-2208300284

amstel78

Problem solved. Car was low on refrigerant.

mrdoofa

I'm having a similar problem with my rear climate control, I think I might try getting it regassed.