116.120 Climate Control Issues: - Page 2 - PeachParts Mercedes-Benz Forum

thorsen · #16 04-24-2011, 09:08 PM

It's a 1980 w116. It has AccII with an UnwiredTools servo replacement. The heater circuit has a ball valve to positively turn it off during the summer. I have the same expansion valve as shown above in post 3. Temperature was measured using my VOM meter with the temperature probe placed against the evap pipe.

Vent temps are around 47-50 degrees as measured with the doors closed and the system on recirculate.

leathermang · #17 04-24-2011, 11:06 PM

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Originally Posted by thorsen

...Vent temps are around 47-50 degrees as measured with the doors closed and the system on recirculate.

Are the windows open ?
Do you have some sort of ' helper fan ' putting air into the front of your car on the condensor ?

thorsen · #18 04-25-2011, 10:37 AM

Windows are closed.

I have the aux fan on and a large fan blowing right on the condenser.

leathermang · #19 04-25-2011, 10:51 AM

So you have a Combo Block TXValve ( as compared to the suction fitting you mentioned earlier ? )just like the rest of us.... ?

You are measuring the temperature at that item with a probe which may be not be ideal for use against a small metal surface..... I am only familiar with using that type of probe for HVAC vents in houses where the entire probe end would be subject to what is being measured.....Is that mentioned somewhere reliable as a legit tool for measuring there ?

Are you measuring at a place between the Evaporator and the TXvalve ? And you are sure that it is the EXIT tube from the Evaporator ?

How about running the test again with the windows open ?

And you are absolutely sure that no hot coolant is making it to the heater core since it is turned off manually ?

thorsen · #20 04-25-2011, 11:20 AM

A picture of my expansion valve is attached. I don't know what type it is.

I doubt my use of the probe is approved in any of the repair manuals, but I was using it more of a relative measure, ie- the suction fitting at the compressor is 22* but the fitting at the evap is 50*.

I am 100% sure I measured the exit from the evap because I checked it before and after the oil return line. The oil return line is the small line from the side of the valve that has a threaded connection on it. It attaches to the suction line after the evap.

I am also 100% sure there is no coolant flow. I checked the pipes leading into the core and they were not hot.

leathermang · #21 04-25-2011, 11:29 AM

So you pretty much have new everything...

What was the situation which caused you to renew most of your AC system ?

Can you get that probe to different spots on the evaporator ?

Have you cleaned or inspected the coils of the evaporator for cleanliness ?

How about trying to find where , relatively, the pfcondensor changes the refrigerant from gas to liquid... hopefully about half way down the coils..

leathermang · #22 04-25-2011, 11:56 AM

In a classical AC system you would have NO parts which are below freezing...
You have a line near the compressor cold enough to make ice...
so the Txvalve... more specifically the siphoning throttle valve part of it was certainly suspect since that is supposed to keep the evaporator from getting below freezing so that ice will not form from the humidity in the air passing across the fins of the evaporator and Stopping air flow....
but here you seem to have it warmer at the exit of the evaporator ... than at the downstream fitting at the compressor... Since the theory is that changing the liquid at the TXvalve to spray into the evaporator is what allows heat to be absorbed from the warm air flowing across the fins... something is clearly wrong.
There is not a physics theory which would allow it to get colder after exiting the evaporator while going along that line to the inlet side of the compressor...
So I am hoping your method of measuring the temp at the exit line of the evaporator is not giving true results... otherwise I am totally out of ' theory ' ....

If on the other hand... your evaporator is dirty enough to keep the warm air from the car from taking away enough cold to operate the exit side of the txvalve... then it is possible for properly cold fluid to exit the evaporator .... along with the possibility the txvalve is not functioning properly.... and the line be below freezing at the inlet to the compressor...

thorsen · #23 04-25-2011, 12:09 PM

Correct, with the exception of the evap everything is new. When I restored the car the AC was inop and out of freon so I replaced everything I could get to. The evap is pretty well hidden and I can only touch a small part of it near the end. I have not cleaned it due to accessibility restrictions. The part I can touch is cool but not super cold.

I have a pretty basic understanding of the theory but I can't come up with anything that fits my symptoms. I was thinking that a partially plugged evap might be the problem but that wasn't explaining my higher-than-should-be low pressure.

leathermang · #24 04-25-2011, 12:15 PM

So at this time... to summarize..

1. We are dealing with a totally new untested TxValve.
2. We might have a dirty evaporator fin condition. ( did you see Dmorrison's thread?)
3. We DO have frost which should not be extant anywhere....
4 We have frost at the wrong place theory wise if your temp at the exit of the evap is true.

I have no theory which fits all your symptoms either ....

" just waiting for Superman or woman to arrive and save the day... "....

thorsen · #25 04-25-2011, 02:04 PM

That summarizes it.

My plan is to remove the evap, but if I go that far I might as well replace it instead of just cleaning it. A new receiver/drier is mandatory and a new expansion valve makes sense too. I'm trying to decide if I should pull the Sanden and put in a Seltec compressor (personal preference) and be done once and for all.

Thanks for your help.

leathermang · #26 04-25-2011, 02:18 PM

Sorry I could not find the answer... I am sure you are going to really examine all the parts as they come out to try to resolve the mystery.....and post anything you find out....

thorsen · #27 04-25-2011, 03:19 PM

Thanks for your help troubleshooting.

The one thing I wasn't sure about - should the sight glass still have refrigerant visible in it when the compressor cycles? Or is it OK that after 3-4 seconds I see bubbles then no refrigerant?

leathermang · #28 04-25-2011, 03:30 PM

If you read over on air condition dot com... and the FSM MB AC manual.. you might just totally ignore the sight glass.... many professionals consider it useless for the purpose of charging the system .... it can be useful for some other purposes but I do not remember which exactly....
There are combos of variables which make it potentially unreliable with regards to bubbles......

Doktor Bert · #29 04-25-2011, 04:20 PM

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