Some AC numbers for the experts to look at - Page 2 - PeachParts Mercedes-Benz Forum

leathermang · #1 06-10-2016, 01:05 AM

Otto, I am talking about OUTSIDE the evaporator... the fins across which the air flows ...
everything else can be perfect... but you can get the effect you describe with a dirty evaporator ...

otto huber · #2 06-10-2016, 01:05 PM

Quote:

Originally Posted by leathermang

Otto, I am talking about OUTSIDE the evaporator... the fins across which the air flows ...
everything else can be perfect... but you can get the effect you describe with a dirty evaporator ...

Yes, I tried that. I don't know how familiar you are with the W126 evaporator, but it rests inside a very narrow channel and faces the firewall. I was able to spray a little bit of coil cleaning foam in there, but I doubt that it did much. I might drop the blower and get back in there with a thin detailing brush and dust off as much as I can. I'll also check to see if the fresh air flap is closing all the way.

leathermang · #3 06-10-2016, 01:09 PM

Quote:

Originally Posted by otto huber

Yes, I tried that. I don't know how familiar you are with the W126 evaporator, but it rests inside a very narrow channel and faces the firewall. I was able to spray a little bit of coil cleaning foam in there, but I doubt that it did much. I might drop the blower and get back in there with a thin detailing brush and dust off as much as I can. I'll also check to see if the fresh air flap is closing all the way.

I assume on our cars that this is one of the worst projects to accomplish.. did you see ' Dmorrison' s ' thread ?... do not remember type of car he has ..but good write up and pics of his cleaning...
and remember to not leave the drain hole in the car plugged with grime..

vstech · #4 06-10-2016, 08:43 AM

keep in mind MB has a freeze switch on the evaporator. if it's relatively mild temps outside, the a/c system operates very efficiently and will RAPIDLY freeze the coil. the compressor would be cycling on and off due to the freeze switch, and your cabin temps would be higher.

otto huber · #5 06-10-2016, 01:10 PM

Quote:

Originally Posted by vstech

keep in mind MB has a freeze switch on the evaporator. if it's relatively mild temps outside, the a/c system operates very efficiently and will RAPIDLY freeze the coil. the compressor would be cycling on and off due to the freeze switch, and your cabin temps would be higher.

Does the signal from the freeze switch travel through the PBU? I ask because I'm using a PBU that was rebuilt by JamesDean here on the forum. Maybe I was getting cold air sooner in the past because of a faulty PBU that wasn't relaying the signal from the freeze switch?

vstech · #6 06-10-2016, 02:20 PM

Iirc, the freeze switch on 126s is above the accelerator and is adjustable.
It breaks the feed to the compressor from the pbu.

otto huber · #7 06-10-2016, 04:22 PM

Quote:

Originally Posted by vstech

Iirc, the freeze switch on 126s is above the accelerator and is adjustable.
It breaks the feed to the compressor from the pbu.

Wow! Just when I thought that I was finally wrapping my head around this complicated HVAC system, you throw out this curve ball.

funola · #8 06-11-2016, 10:16 AM

Quote:

Originally Posted by otto huber

Wow! Just when I thought that I was finally wrapping my head around this complicated HVAC system, you throw out this curve ball.

I think this is the freeze switch mentioned, MB calls it "A/C Temperature Sensor for Evaporator, (ETR Switch)"

http://www.pelicanparts.com/catalog/SuperCat/W123/MBZ_W123_VENTAC_pg1.htm

Here's an interesting post on modifying it A/C modified: ETR-switch from Maytag

funola · #9 06-11-2016, 10:28 AM

Here's a good article on the ETR on a R107, with a great explanation on how it works. Mercedes-Benz R107 A/C Temperature Sensor ETR Switch Replacement | 1972-1986 - 450SL, 380SL, 500SL, 560SL | Pelican Parts DIY Maintenance Article

otto huber · #10 06-11-2016, 02:12 PM

Based on my cars ability to accelerate, it's pretty obvious when my compressor clutch is engaged, and from what I can tell it's always cycling as long as I have the AC turned on.

leathermang · #11 06-10-2016, 05:16 PM

There are a lot of posts in this thread which state a certain weight of refrigerant WITHOUT stating the EXACT REFRIGERANT being talked about... which can vary due to the physics of that Refrigerant.....
Everyone should double check before installing... as too much is really bad news... an AC system can operate several oz under the ' max ' load just fine... but ONE OZ over is a problem...

leathermang · #12 06-12-2016, 12:04 PM

That is great news Otto....

dennislarock · #13 06-12-2016, 02:54 PM

Ditto... the most bang for A/C is to clean the evaporator ...I removed the dash to clean mine. HUGE HUGE HUGE difference in performance
.