Strange AC behavior: CCU? - Page 3 - PeachParts Mercedes-Benz Forum

leathermang · #31 06-26-2011, 01:07 PM

Quote:

Originally Posted by Goldenvoice

It's not quite the blind leading the blind, but has had it's moments

How, pray tell, do I get into the evaporator?
And best method to clean?

I also plan to remove the ACC unit, and find those pesky little relays, and give their contacts a cleaning. Not sure I need to resolder the whole works, but will give it a thorough visual inspection.

Curious: at what point, or in what setting does the system go to 'recirculate' air?

And as far as the pencil thermometer and ACC settings, I roll the temp wheel to Min (clicks), but the fan is either on full, off, or auto (which steps up to high).

I did not promise you this would be easy... pretty much the opposite... but sometimes there is no choice...

There is a thread by Dmorrison about cleaning the inside of the evap where the fins are...and others have done it... but on your car I don't know which route to suggest is easier..

The other questions are not about type one AC .. only type one is simple enough for me to deal with it... that dash unit I think you are talking about... the diagnostics alone run 80 pages in the paper MB AC FSM...

whunter · #32 06-26-2011, 03:27 PM

Quote:

Originally Posted by leathermang

I did not promise you this would be easy... pretty much the opposite... but sometimes there is no choice...

There is a thread by Dmorrison about cleaning the inside of the evap where the fins are...and others have done it... but on your car I don't know which route to suggest is easier..

The other questions are not about type one AC .. only type one is simple enough for me to deal with it... that dash unit I think you are talking about... the diagnostics alone run 80 pages in the paper MB AC FSM...

Replacing the A/C Evaporator
on the 1983 240D & 1982 300TD (W123)
by dmorrison
6/17/06
http://www.peachparts.com/Wikka/W123Evaporator

leathermang · #33 06-26-2011, 03:31 PM

Thanks Roy.

Goldenvoice · #34 06-26-2011, 04:48 PM

Wow, what a great photo-essay - now THATS an involved process - one I don't think my patience will allow at this point, but a great way to understand the layout of the heating/cooling system.

Does make me wonder, though, if my evaporator looks similar, or worse; causing the lower than one would expect airflow... esp since by design, the regular use of the AC system would keep the evaporator washed clean (theoretically), but when the system has been dysfunctional for many years, lord knows.

Dang, too bad the fins don't face to allow one to drop the fan, and hit 'er with a garden hose and squirter (tongue in cheek - but farm-boy thinking...)

'course, it does have a drain out the bottom, yes/no?

leathermang · #35 06-26-2011, 04:52 PM

Quote:

Originally Posted by Goldenvoice

....since by design, the regular use of the AC system would keep the evaporator washed clean (theoretically), ...
'course, it does have a drain out the bottom, yes/no?

You are making stuff up... no way it is washed clean by use...
yes, has drain and you had better make sure it stays open..or a terrible fish smell can overtake your car....

I have thought about examining to see if there is some way to stick a garden hose down the center vent.... to avoid that nightmare procedure doing it correctly....

Goldenvoice · #36 06-26-2011, 05:05 PM

Quote:

You are making stuff up... no way it is washed clean by use...

Read that somewhere - seemed odd to me too (but an interesting theory, all the same - and mixed with humor, 'case ya missed it)

Quote:

I have thought about examining to see if there is some way to stick a garden hose down the center vent.... to avoid that nightmare procedure doing it correctly....

Agree it's worth some thought. I try to be practical with my time. I appreciate doing it correctly, but within reason. I even pictured some sort of high-volume air source, blown in one of the output ports, with the others blocked off... silly, but when I look through those photos, I shudder...

leathermang · #37 06-26-2011, 05:11 PM

That was not a theory... it was magical wish fullfillment pain avoidance thinking...

I think the book flat rate manual is 17 hours for taking the dash off..
and we had one college student in Florida that did it twice in a row...
shudder....

Goldenvoice · #38 06-26-2011, 05:44 PM

Give that student an A!

leathermang · #39 06-26-2011, 05:47 PM

I gave him an OCD.

Goldenvoice · #40 06-26-2011, 06:37 PM

LOL - Thanks - I needed that!

Goldenvoice · #41 06-27-2011, 11:50 PM

Did a full re-solder and sanded-polished relay contacts in the CCU today. Wow, it does things I never knew it would do - seems to work great. The 2 buttons next to off didn't run the fan - now they do...

PLUS - the fan seems to run faster than before - but that's an un-scientific opinion.

Back to the AC: I'll order up a new expansion valve, as mine is confirmed to have a small leak.

It also still has this issue: the clutch doesn't seem to want to engage - at least positively, unless I jumper around the low pressure switch on the dryer. Should I, perhaps, just order up a new switch, so as to eliminate that as a potential problem?

It wouldn't run mid-week, so during diagnostics, I jumpered around the switch, and it ran (clutch) every time. The tech hooked his gauges up, and the 'relaxed' pressure was around 60 lbs - shouldn't that be enough to let the clutch engage? (confusion is the tech says the switch is fine:| )

tangofox007 · #42 06-28-2011, 06:03 AM

Quote:

Originally Posted by Goldenvoice

I'll order up a new expansion valve, as mine is confirmed to have a small leak.

That is not an uncommon problem. It might not go away with a new valve. Be mindful that sniffers can detect leak rates on the order of a fraction of an ounce per year.

Quote:

Originally Posted by Goldenvoice

Should I, perhaps, just order up a new switch, so as to eliminate that as a potential problem?

I sure would, if I was going to open the system for any other reason.

Quote:

Originally Posted by Goldenvoice

The tech hooked his gauges up, and the 'relaxed' pressure was around 60 lbs - shouldn't that be enough to let the clutch engage? (confusion is the tech says the switch is fine:| )

10 psi should be enough to close the switch.

Goldenvoice · #43 06-28-2011, 10:08 AM

The expansion valve: sniffer picked it right up, but also, there was dye - enough to show it had actually formed a drip. We cleaned off the dye, and after the 20 mile trip to town and back, there was the dye around the cap threads again...

But yes - great, I'll keep in mind a good sniffer 'may' detect even on the new valve !

Back to the idea of cleaning the evaporator...