R107 - is it necessary to remove instrument panel to R/R expansion valve? - PeachParts Mercedes-Benz Forum

nhdoc · #1 07-07-2006, 12:00 PM

It looks like I have a clogged expansion valve on my ACC, the compressor works but the low side draws about 7 PSI of vacuum with a full charge (high side spikes after startup but settles at 130 or so). I replaced the receiver dryer hoping it was the point of constriction but now it does the same thing and when trying to blow air through the TXV line all I got was a small flow...looking at the CD it looks like MB says to remove the steering wheel and instrument panel to get to it...is there any way to get at it from below or is it absolutely necessary to remove those to get to it?

KCM · #2 07-07-2006, 02:13 PM

I suppose anything is possible, but it is much easier to remove the cluster and then you get a clear view of the valve. On the air bag equipped cars, you need to unhook the red connector under the floor mat in the passenger footwell (behind the black plastic cover), then unhook the battery cable. A torx socket is need to remove the air bag as well. Remember to mark the steering wheel in reference with the steering shaft mark in order to get the steering wheel in the same location, as it probably has no marks from the factory. After the steering wheel is off, it is a piece of cake to take the cluster out.

There is a filter in the inlet to the valve which is most likely plugged. Your valve is likely okay otherwise. It might be possible to get the inlet hose off from under the dash to get the screen out, but again it is a real pain to see much up there with the cluster installed.

nhdoc · #3 07-07-2006, 04:37 PM

Thanks...yeah my car has the airbag which is why I was reluctant to remove the wheel...oh well...life's an adventure!

Thanks for the tips on the valve itself too...the part is cheap enough that I may just replace it anyway but I'll see what I can see in the inlet.

nhdoc · #4 07-07-2006, 10:17 PM

By the way, is the screen at the inlet of the expansion valve removable for cleaning?

TheV12pwr · #5 07-07-2006, 11:02 PM

There is nothing wrong with your expansion valve!
Your high pressure is low, it should be about 200 psi and your low pressure is low ,it should be about 35 psi.
Use proper equitment to cnarge the A/C and always pull vacuum first,watch the high pressure,charge untill above 200-220 psi.
Let us know how it worked out!

nhdoc · #6 07-08-2006, 08:10 AM

Quote:

Originally Posted by TheV12pwr

There is nothing wrong with your expansion valve!
Your high pressure is low, it should be about 200 psi and your low pressure is low ,it should be about 35 psi.
Use proper equitment to cnarge the A/C and always pull vacuum first,watch the high pressure,charge untill above 200-220 psi.
Let us know how it worked out!

Nope, there is nothing worng with the charge...the problem is a restriction in the system, which I thought might have been the receiver-drier but is in the expansion valve. There is a full charge now in it...I know this because I put it in, 2.2lbs of R12 (3 12 oz. cans). I evacuated the system after replacing the R-D and before I put the 3 cans in. The reason the high side is low is because the compressor is "starved" due to a clog (presumably at the valve). It can't build high pressure because there is nothing to pressurize coming into the suction side. The reason the high pressure spikes right after the compressor comes on is because then there is some gas on the low side (after both sides equalize) but once that is pumped through the compressor is pulling a vacuum and is starved. It actually is only pulling 7 PSI of vacuum...not 14, the vacuum side reads in inches of Mercury not PSI upon further examination...

KCM · #7 07-09-2006, 11:52 PM

Quote:

Originally Posted by nhdoc

By the way, is the screen at the inlet of the expansion valve removable for cleaning?

Yep, and available (though expensive) from Mercedes.

nhdoc · #8 07-11-2006, 07:32 AM

Hmmm...the EPC I have shows no separate part for the screen...you don't happen to have a part number, do you?

How expensive can it be??? the entire expansion valve can be bought for around $40 so I can't think the screen would be more than $10 maybe.

I've got a tank coming in to recover my R12 into and then I will tackle the TXV...I downloaded all the instructions from alldata on how to remove the airbag and instrument cluster...it does not look too bad. Once I get the tank in I am good to go with it...

nhdoc · #9 08-08-2006, 11:16 PM

Today was D-Day on this project. Removing the steering wheel and instrument cluster was no problem, except the TIGHT bolt holding the wheel on (had to use an impact gun on it to loosen). Removing the old expansion valve was a bear...the guy who said you have to be a contorsionist was right! The good news is I got the new one in and the old was definitelty clogged (it had no screen in it but I could see it was completely plugged at the inlet). I blew compressed air through the hose from the receiver drier to clear it before installing the new valve (with screen this time).

I'm very confident I'll have cold air coming out...the old valve was surely the culpret!

Richard Wooldridge · #10 08-15-2006, 10:12 AM

Hi NHDOC, how about an update on this - do you have cold air yet? Or are there additional problems? Interested parties would like to know!

nhdoc · #11 08-16-2006, 07:35 PM

Quote:

Originally Posted by Richard Wooldridge

Hi NHDOC, how about an update on this - do you have cold air yet? Or are there additional problems? Interested parties would like to know!

Yes, 38 dgerees out the vents for a week now! Thanks for asking. The expansion valve was definitely the problem. It started to cool after less than one can of R12 was in it...unlike before where it would not cool at all no matter how much is in. As long as I don't have a leak at the connections I broke open I am home-free.

So far, so good