116.120 Climate Control Issues: - PeachParts Mercedes-Benz Forum

Doktor Bert · #1 08-24-2009, 09:37 AM

Good Morning!!!

Wanted to pick your collective brains for a few....

On my 116.120, I have been driving it with the A/C discharged for the past few months. The A/C worked perfectly before my sons' accident in 2006. I taped off the lines while the car was in storage and I have been driving it again since June of 2009.

I have had the compressor unhooked (front seal leak) but the blower would always switch to high speed when you flipped the compressor switch on. The weather has been getting hot, so I decided to fix it....the right way.

I installed a new aluminum billet climate control unit, amplifier, schrader valves, auxiliary water pump, receiver drier, condenser and compressor recently. All of the blower speed functions are perfect and all of the vents are working properly. Late last night, I hooked up the compressor and flipped the switch and blew #9 fuse. I double checked the clutch coil and it works fine and the amperage to apply the clutch is within spec. Now, the high speed blower is on all the time (when you have the A/C turned on that is) and I am getting no current to the A/C clutch coil, but #9 fuse has continuity. Everything else in the climate control system is working perfectly. Is there a relay that controls this???? I can't find any service information on this thing so I am kind of puzzled.

Also, I charged the A/C with R-12 and the correct amount/type of oil, but once I got the compressor running, the low pressure side went into a vacuum. No noise, no clutch slippage, just 28 in/hg of vacuum on the low side. My guess is the expansion valve must be stuck....at least I think the 116 used an expansion valve, so it looks like that will be my next project, unless it decides to unstick itself....:-)

I really appreciate all of your time...Robert

Doktor Bert · #2 08-24-2009, 01:48 PM

After studying the wiring diagram, I am puzzled as to why I experienced an overheated #9 fuse when I switched the compressor on for the first time since the April 2006 collision.

The Amplifier receives a signal from the compressor manual switch, which it then uses to increase blower speed. However, the rest of the compressor clutch circuit is quite simple and is totally independant of the servo/amplifier.

Basically, the clutch coil manual switch is fed from the #9 fuse (8 amp) through an ambient temperature switch (behind glovebox in W116) through the low pressure cut-off switch (drier mounted W116) through the evaporator temperature regulator (above throttle pedal W116) and to the clutch coil.

IIRC, The clutch coil will operate no matter which side you apply power or ground to, which I confirmed through testing with the clutch coil unhooked from its 2-wire harness and nonw of the wiring at the amplifier or servo is heavy enough to power the clutch coil.

Still pondering this one....

Doktor Bert · #3 04-22-2011, 12:24 PM

The cause of the blown #9 fuse was a shorted A/C low pressure switch.

Problem solved!!!

The cause of the vacuum on the low pressure side of the A/C was traced to the expansion valve, which was stuck closed.

It took about 15 minutes to remove the cover under the dash that extends from the lower edge of the instrument panel, down to the brake pedal. The valve only took 30 minutes to replace after that.

The expansion valve I used was a P/N 115 835 00 72.

I used a 17mm, 15mm and 15/16" end wrench to change the valve. The fittings on the expansion valve each have a cone shaped copper sealing washer, which I re-used. The old drip tape was still pliable, so it was removed, rolled out flat on a section of cardboard with a rolling pin and re-installed.

TECH NOTE: make certain your capillary tubes clear the ducting for the LH outside dash vent AND the linkage on the accelerator pedal.

Hope this helps...Robert

Doktor Bert · #4 04-23-2011, 11:56 AM

Anyone with a W116 ever attempt to adjust the ETR without remove the dash?????

Doktor Bert · #5 04-24-2011, 02:27 PM

Not easy to get to, but you can adjust the ETR through the glovebox opening with a carburetor adjustment tool.

I charged the system with R-12 using the sightglass method and was rewarded with 40 psi on the suction side @ idle and about 10 psi at 2500 rpm. Vent temps were 49° and steady on a 70°F day with 45% humidity, which is within the spec according to the climate control manual.

A slight adjustment to the ETR brought the vent temps down to 37°F under the same ambient temperature conditions.

Hope this helps...Robert

thorsen · #6 04-24-2011, 02:47 PM

Bert,
What procedure did you use to adjust the ETR? I assume there is a screw switch you can turn?

Also, any idea how to tell if the expansion valve is stuck open?

Doktor Bert · #7 04-24-2011, 03:12 PM

Thorsen.

If the expansion valve sticks open, you will have no pressure differential on the gauges.

If it sticks closed, like mine, you will see the low side go into a deep vacuum.

The ETR has a felt cover. There is a small screw under it. I turned it just a bit and could watch the temp gauge drop.

leathermang · #8 04-24-2011, 03:18 PM

Quote:

Originally Posted by Doktor Bert

.....I charged the system with R-12 using the sightglass method ......

Others reading this should keep in mind that the MB AC FSM WARNS against just using the sight glass as the method for filling because it can give erroneous readings...and result in overfilling...which can cost you a lot of money to redo.

Since the OP appears to have gauges and used them.... I do not understand why ' the sight glass method ' would be used... as gauge readings /measuring the charge are the normal safe ways to do this...
Perhaps he charged up and then checked afterwards ?

Doktor Bert · #9 04-24-2011, 03:24 PM

Quote:

Originally Posted by leathermang

Others reading this should keep in mind that the MB AC FSM WARNS against just using the sight glass as the method for filling because it can give erroneous readings...and result in overfilling...which can cost you a lot of money to redo.

Since the OP appears to have gauges and used them.... I do not understand why ' the sight glass method ' would be used... as gauge readings /measuring the charge are the normal safe ways to do this...
Perhaps he charged up and then checked afterwards ?

Leather,

I understand and I have read that passage too. I think it is one of the many 'fail safes' that MBZ prints into their publications as a precaution.

I started out working in a Pontiac dealership in 1979 as a mechanic's helper. Over the years, we never charged an A/C system using anything other than the sightglass method, because we were paid by the flat-rate hour and time was money.

Over the years, I have checked pressures after the fact and they were always right on the money, so I just stoped checking them.

Even when I worked for the BMW and MBZ dealer, we used the sightglass method until they stopped putting sightglasses in the cars.

After that, we simply dumped in a static charge by weight, closed the hood and drove the car. If the vent temps were within spec, according the the FSM, the job was complete. Putting the charge in by weight is even faster.

The vent temps will not be within spec with an under or overcharged system.

leathermang · #10 04-24-2011, 03:28 PM

I do not care what you do with or to your car...
notice my post was not directed to you..
it said ' to others reading the post' ...
and told the truth about the warning in the MB AC FSM ....
which is a totally legit thing to post about the time someone says they used the sight glass as they way they charged their car....

Doktor Bert · #11 04-24-2011, 03:32 PM

Quote:

Originally Posted by leathermang

I do not care what you do with or to your car...
notice my post was not directed to you..
it said ' to others reading the post' ...
and told the truth about the warning in the MB AC FSM ....
which is a totally legit thing to post about the time someone says they used the sight glass as they way they charged their car....

Your truthfulness has never been in question with me. I'm just telling you what I did and why it works.

I would not discourage anyone from weighing the charge or checking the pressures. After a few thousand services over 20 years, I just charge it and check the vent temps.

Funny...all the years I worked in the dealer, I never saw anyone set the timing on a 617 with a dial indicator, they just lined up the marks. I do not advocate that either, but my point is this.

I doubt you get your charge weighed and pressures checked at the dealership. I have watched them dump in whatever the tag says and then drive the car out of the bay. NEXT!!!!

In my case, a clear sightglass corresponded to correct low side pressures (high side wasn't checked) and the vent temp was within the specs in the FSM for the relevant atmospheric conditions.

Doktor Bert · #12 04-24-2011, 03:44 PM

Not too long ago, I took an old junk R4 compressor and pushed the band off that makes up the body of the compressor,

I sawed a couple of notches in it, to clear the bolt bosses and retaining tab, then split the band in one spot with a die grinder. I then tack welded the split together, so the band can be used to press the band on and off, allowing you to change the 2 large 'O' ring seals on the compressor body.

I have a press, but did it in the vise with a couple of long bolts and some washers.

I will post some photos of this later if you all find this of interest.

Happy Easter!!!!....Robert

leathermang · #13 04-24-2011, 04:25 PM

Quote:

Originally Posted by Doktor Bert

..... I'm just telling you what I did and why it works......

I will bet that you do not even KNOW what the conditions are which might cause the sight glass to indicate ( by still having bubbles ) more refrigerant was needed ( when it is actually full ).

Come on !!! it is an open book test and I will bet you can not even find and tell us what they are.....

If you did know them...( very unlikely.... given your defense of ' I have been doing it this way for x number of years and it worked for me ' ) how simple and KIND it would have been to list them when you said that...

" I have been lucky over the years not to have had any problems overcharging AC systems using the sight glass method... even though this method is warned against in the MB AC Factory Shop manual ..

BUT is it possible under A plus J plus X conditions to get a false reading and you wind up with too much refrigerant in your system " ...

SO EASY !!! SO SMART AND KIND to others who might not have the background to understand that you are depending on luck instead of what the makers of your car go to the trouble of researching and printing in the instruction manual....

thorsen · #14 04-24-2011, 08:05 PM

What do you think about this problem with my W116's AC with R-12?

At 65* ambient at 1800rpm, the high is 150 (which is correct according to my R-12 chart) but the low is 24 (it should be about half that).

The sight glass has no bubbles during operation but when the compressor cycles after 3-4 seconds you see bubbles then the sight glass is open - meaning you see no bubbles nor refrigerant.

Also, the suction fitting at the compressor is covered in ice but the suction fitting at the evap is only about 50*.

Additional information - compressor is a new Sanden rotary, condenser is a new parallel flow, expansion valve and hoses are new.

leathermang · #15 04-24-2011, 08:17 PM

Thorsen, If you are addressing that question to me....
1. What year is that 116 ?
2. What type AC does it have ? ( type one,two, or three or ' other' ? )

I only have books for the 123 models ( not counting the mb and three generic AC manuals ) ...and pretty much 1980-85 and specialize in the type one my car has because the diagnostic section of the AC manual for my wagon's DASH BUTTONS ALONE was 80 pages long...

Why is it you are giving ambient air temperature but not any vent temperatures ?
When you do check the vent temperatures....are you following all the rules Vstech mentioned for proper conditions ?

Can you post pics of your dash to see if we can identify the AC type ? and inside of the engine compartment ( does it have that fiberglass monstrosity for instance ? ).

Are you saying that you have a throttle suctioning valve instead of a block TxValve ? How are you measuring that temp there ?