1995 E300D AC Question - PeachParts Mercedes-Benz Forum

tankowner · #1 06-13-2011, 09:38 PM

Hey Gang,

Question on the AC - mine has been acting up and I am trying to determine where exactly the problem is. Inside the cabin, the air will blow cool for a few minutes and then it warms up - it will continue this cycling off and on. I assumed the compressor was cycling on and off, but now I am not so sure. I put the gauges on it tonight to checked out the pressures. The low side pressure hovers around 30-35, so that seems reasonable. And the high side is also in the 175-180 range, which sounds good. However, there is intermittently an audible change (sort of like the engine dogging down a little like when the AC compressor kicks on - but the compressor was running and continued to run throughout this process) that is accompanied by the high side pressure climbing up to 250. Right about the time the high side pressure gets to 250, the sound switches back and the pressure lowers back to normal. Again, the clutch is engaged and spinning throughout this whole time. The low pressure line is cold with condensation on the outside. Plenty of condensate dripping from the underside of the car. The air from the vents is cool but I don't think as cold as it should be - seemed to be hovering around 65 F, so it could definitely be colder.

I have some thoughts, but I'd like to know: What does this sound like to you guys?

Any help appreciated!

leathermang · #2 06-13-2011, 09:58 PM

There is the potential with that symptom of your TXvalve not working properly... specifically the suction throttling valve section of it... allowing your evaporator to get below 32 degree F.... thus freezing the humidity in the air on the fins of the evaporator... cutting off your cooled air....until it melts... allowing it to once again cool for a little while...

tankowner · #3 06-13-2011, 10:30 PM

Quote:

Originally Posted by leathermang

There is the potential with that symptom of your TXvalve not working properly... specifically the suction throttling valve section of it... allowing your evaporator to get below 32 degree F.... thus freezing the humidity in the air on the fins of the evaporator... cutting off your cooled air....until it melts... allowing it to once again cool for a little while...

Thanks, leathermang. Yeah, the TXvalve was one of the things I was thinking of as well. I also considered that there might be air or moisture in the system.

The PO had the evap replaced - that was 3 years ago. I have receipt of the work, but no real knowledge of what all was done then. I have considered that when it was replaced, the receiver/dryer may not have been replaced and/or the system was not properly evacuated then - so perhaps air/moisture in the system.

At the same time, I see what you are saying about the valve. The first year I had this car, it would randomly blow little bits of frost/ice out of the vents. Which I think would be consistent with what you are saying.

I am thinking that a good approach here would be to replace the expansion valve and the receiver/dryer. Then evacuate the system real good and recharge. What do you think? Anything else to consider or do at the same time?

Thanks again!

Edit: I located the expansion valve at the firewall, looks a little challenging to get at - but at least it's not buried in the dash!

leathermang · #4 06-13-2011, 10:44 PM

That sounds good to me.... BUT
I do not have any manuals for your car..
so perhaps someone will post adding other possibilities to what might be the cause...
but the ' blowing ice' is certainly suspect... LOL
Not a total clincher since the conditions for freezing vary from 32 degrees sometimes..

tankowner · #5 06-13-2011, 10:59 PM

Quote:

Originally Posted by leathermang

That sounds good to me.... BUT
I do not have any manuals for your car..
so perhaps someone will post adding other possibilities to what might be the cause...
but the ' blowing ice' is certainly suspect... LOL
Not a total clincher since the conditions for freezing vary from 32 degrees sometimes..

Appreciated, thanks.

I'll give this a try and see where it gets me. I realized shortly after I bought the '95 that something wasn't right about the AC (of course it seemed fine on the test drive

) - I soon found that the KLIMA had been installed upside-down at some point and slowly filled with water (probably over time from condensation) - what a mess inside! I replaced that, which helped a lot - but things have always been a little off. Coming off a high of replacing the condenser in my wife's minivan last weekend, I figured it was time to tackle this one. Wish me luck.

leathermang · #6 06-13-2011, 11:18 PM

I do wish you the best of LUCK.
But suggest you attempt to find actual MB AC service manual for YOUR CAR before proceeding...
Applying a ' high ' from one vehicle to working on another..... can really cost you when reality collides with that ( false ) momentum....

tankowner · #7 06-14-2011, 03:25 PM

Quote:

Originally Posted by leathermang

I do wish you the best of LUCK.
But suggest you attempt to find actual MB AC service manual for YOUR CAR before proceeding...
Applying a ' high ' from one vehicle to working on another..... can really cost you when reality collides with that ( false ) momentum....

Sage advice, indeed. I do have the FSM procedure for replacing the TXvalve and recharging the system. I don't think much harm can be done from replacing the valve and receiver - evacuating the system and recharging. However, I have been wrong before. No matter, I won't hold anyone else accountable.

Thanks for the input, I will let you know how it turns out.

leathermang · #8 06-14-2011, 04:26 PM

No harm... I was just saying there might be other parts to your late model car which could cause that symptom which I do not have a manual for... and I have no idea how easy or hard getting to that TxValve might be ....easy on your 123 but a question mark for the other one...wish someone with experience on your model would stop by...

engatwork · #9 06-14-2011, 04:35 PM

It does sound like the evap could be freezing up. Has any work been done to it lately?

tankowner · #10 06-14-2011, 11:34 PM

Quote:

Originally Posted by leathermang

No harm... I was just saying there might be other parts to your late model car which could cause that symptom which I do not have a manual for... and I have no idea how easy or hard getting to that TxValve might be ....easy on your 123 but a question mark for the other one...wish someone with experience on your model would stop by...

I did locate the TXvalve . . . it's near the firewall on the driver's side. Perhaps a little tricky to get at, but we'll see how it goes. I'll take some pics and post them for those interested.

tankowner · #11 06-14-2011, 11:55 PM

Quote:

Originally Posted by engatwork

It does sound like the evap could be freezing up. Has any work been done to it lately?

No, not lately. Looking back at the paperwork the PO gave me at the time of sale, I see that he took it to an indy that did a leak test on the system. So obviously the was some issue. Not sure what the outcome was, but 3 months later the same shop installed a new evaporator to the tune of $1300. The only parts listed on that receipt are the evaporator and freon. That was about a year prior to my purchasing. Like I mentioned earlier, the AC seemed fine on test drive back then, so I didn't suspect anything and was happy the evap was new. But after some time I realized it wasn't working quite right. In looking around I found the KLIMA installed wrong and full or water - the circuit board was rusting! I replaced that, which improved matters - yet I'm still stuck with the current situation. I question that they didn't replace the receiver at the same time. And I don't really know the shop very well, so I wonder about air/moisture in the system. Given that the evap apparently freezes up sometimes, I think it is at least worth replacing the TXvlave and receiver. Then evacuating the system really good and recharging.

If anyone has other suggestions, I am open to all ideas. I give this idea a shot this weekend and see what I get. Thanks!

engatwork · #12 06-15-2011, 07:22 AM

I'd start by hooking the machine up to it, removing all the freon, flush the system and then add oil, vacuum it down and recharge.

vstech · #13 06-15-2011, 09:34 AM

Quote:

Originally Posted by tankowner

Hey Gang,

Question on the AC - mine has been acting up and I am trying to determine where exactly the problem is. Inside the cabin, the air will blow cool for a few minutes and then it warms up - it will continue this cycling off and on. I assumed the compressor was cycling on and off, but now I am not so sure. I put the gauges on it tonight to checked out the pressures. The low side pressure hovers around 30-35, so that seems reasonable. And the high side is also in the 175-180 range, which sounds good. However, there is intermittently an audible change (sort of like the engine dogging down a little like when the AC compressor kicks on - but the compressor was running and continued to run throughout this process) that is accompanied by the high side pressure climbing up to 250. Right about the time the high side pressure gets to 250, the sound switches back and the pressure lowers back to normal. Again, the clutch is engaged and spinning throughout this whole time. The low pressure line is cold with condensation on the outside. Plenty of condensate dripping from the underside of the car. The air from the vents is cool but I don't think as cold as it should be - seemed to be hovering around 65 F, so it could definitely be colder.

I have some thoughts, but I'd like to know: What does this sound like to you guys?

Any help appreciated!

I bet the noise you are hearing is the aux fans engaging and disengaging.
clean your condenser...

leathermang · #14 06-15-2011, 09:44 AM

I wonder if the path from one of your vents to the AC evap fins ( top side) is clear enough to stick one of those Harbor Freight ( others make them but more expensive ) snake inspectors... when they went to $99 on sale I got one for the PTO work on my tractor.. I am impressed with the quality of the image... even has a removable screes..wireless !! if you had that looking ( has light ) at the fins when this happened it might show ice... or it might not if it was down inside and you did not have a good lineup on the fines...

tankowner · #15 06-15-2011, 06:05 PM

Quote:

Originally Posted by vstech

I bet the noise you are hearing is the aux fans engaging and disengaging.
clean your condenser...

You know, I can't say that isn't it, I will have to go hook up the gauges and then watch the fans. I don't think that is the noise, though. My question would be . . . why the fan engaging/disengaging cause the highside pressure to rise to 250?