[W126 Coupe] Suspect pressure switch issue on the receiver dryer

[Dick Spellman]

Hi Markus and for the lists benefit (maybe),

That 2 pages of the manual was of help.  The pressure switch is open 
until sufficient pressure is reached then it's supposed to be closed 
permitting this one leg of the compressor circuit to be closed at all 
times.  I simply jumped the two leads on the harness after running the 
prescribed tests in the manual first.  Placing the jumper engaged the 
compressor clutch and I was able to complete the fill to correct low and 
high side pressures and confirm the system had no other issues based on 
the values obtained.

Put the caps on the service ports and road tested for 15 minutes 
obtaining 45 F then added a tad more refrigerant and got a steady 40F at 
the vents.  I was in process of removing the service port cap on the 
high side when I heard a gas release as the cap came free and noted a 
deposit of dye.  I had wiped this whole area clean on the button up.  
*So, the NEW R-134 high side service port schrader valve is a piece of 
crap.*  I'll have to evacuate the darned system all over again to 
replace this one port which will slowly allow all of the refrigerant to 
escape if I do not make the repair.

Anyway, I figure I will get down to 38-40F no problems based on the 
earlier tests once the port is replaced. So, for anyone doing a fill 
there may be a remote chance that you will need to jumper the pressure 
switch leads in order to get the compressor clutch to engage and 
complete a fill.  This was the first time I have encountered this and it 
may be that the new pressure switch is a bit too high.  I'll know soon 
enough since I now have to repeat the entire process.

Regards,

Dick

Markus Meyer wrote:

> Dick

>  

> Maybe this will help?  Is this car an 86, I may have another file that 

> will help if this one doesn't...

>  

> Good luck,

>  

> Markus Meyer

> mfm at meyerprobateproperties.com <mailto:mfm at meyerprobateproperties.com>

> www.meyerprobateproperties.com <http://www.meyerprobateproperties.com>

> Meyer Probate & Properties, LLC

>

> 484-919-9762

>

>     -------- Original Message --------

>     Subject: [W126 Coupe] Suspect pressure switch issue on the receiver

>     dryer

>     From: Dick Spellman <spell.yy at verizon.net>

>     Date: Tue, June 17, 2008 5:58 pm

>     To: Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>

>

>     Hi Jonathan:

>

>     Got everything buttoned up, vac'd things down, started the load with

>     R-134 and stopped when high side static pressure hit 100lbs at 80F.

>     Compressor would not kick in! I suspect it's the new pressure

>     sensor on

>     the new r/d since that is the only wiring I removed and then

>     re-attached. The other sensor with leads is for the fan on/off

>     based on

>     temp if that's correct. But, I don't use this switch where I have the

>     relay to kick the fan when the compressor clutch engages as per Stu

>     Ritter. Been working fine that way for years.

>

>     Questions.

>     Anyway to test that pressure switch?

>     Is it normally open (N.O.) or normally closed (N.C.) when it reads

>     pressures as OKAY?

>     Is this switch reading both high and low or just low pressure when it

>     actuates?

>

>     With this bit of info I can either remove a lead opening a closed

>     circuit or jumper the two leads to close an open circuit. Then I will

>     proceed with the fill procedure once again. Kinda need to know how

>     the

>     switch performs before I load more refrigerant in the system.

>

>     Any info will be of help.

>

>     Thanks,

>

>     Dick

>


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