[W126 Coupe] a/c question - UPDATE

[Dick Spellman]

Hi Markus:

So was it the KLIMA relay, the wiring harness or the speed sensor that 
had failed?  And what did Jonathan suggest in detail?

Regards,

Dick

Markus Meyer wrote:

> Actually Dick, on a suggestion from Jonathan, I tried something else 

> first.  I rewired the wires for the Klima relay and replaced with a 

> new relay, and knock on wood, been working fine for two days now.  

> Seems the issue was the speed sensor on the back of the compressor....

>  

> Cheers,

>

> 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 --------

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

>     Date: Sat, September 22, 2007 1:28 pm

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

>

>     Hi Markus:

>

>     Nice bit of troubleshooting step by step!  I'd say you have

>     already answered your question.  If the compressor continues to

>     operate (clutch stays engaged) but, the high side is dropping as

>     you indicate, it's probably the expansion valve.  You'll need to

>     vacate the system of it's current R-134a charge (let someone use a

>     machine to capture rather than let the system blow off into the

>     atmosphere), replace the expansion valve (loads of fun) then

>     install a new receiver/dryer as the last step in closing up the

>     system.  Vac it down, let it sit to see the vacuum levels hold for

>     an hour or so,  add the R-134 with oil (1 ounce per can) and

>     expect you will need 2 cans +/- total.

>

>     Only other comments are to vac as soon as possible after buttoning

>     the system up to rid the system of any moisture (something the new

>     r/d won't have to deal with) and use gauges to set the volume of

>     R-134 correctly.  At least that's all I'd do.

>

>     Dick

>

>     Markus Meyer wrote:

>>     Hi gang,

>>      

>>     I have a 300SEL (W126) that I acquired recently that has been

>>     acting up with the air conditioning.  I swapped out the

>>     pushbutton unit with another SEL I have sitting around, that

>>     didn't do anything.  I did some testing per the W126 manual and

>>     thought I had narrowed it down to the Klima relay, but that

>>     didn't help either.  Today I was at the dealer getting some brake

>>     paste and antenna grommets (items still rather inexpensive at the

>>     dealer if you can believe that) and a tech was working on a car

>>     there, so when I was done I stopped and chatted with him.  He was

>>     kind enough to let me borrow his guages, so I hooked them up to

>>     see what was going on.

>>      

>>     Bit of background:  a/c has worked for an hour or so at a time

>>     occasionally, works in park/idle just fine and then seems to cut

>>     out after driving for a few minutes or so, other times takes

>>     longer - 10 minutes or an hour.  Nothing seems to make it come

>>     back on besides shutting the car off for a minute or two and

>>     retrying.  I don't think its the ignition switch because

>>     everything else is fine (blower motor continues to blow air, just

>>     not a/c air) and jiggling it did nothing for the a/c.   Oh yeah,

>>     car was converted to R134a, and I don't know what they replaced

>>     besides the compressor which is obvious.  Receiver/dryer may not

>>     have been replaced as it looks older and still has the sight

>>     glass which I understand the R134a systems do not have.

>>      

>>     Okay.  So at the dealer, in park/idle, pressures fluctuated on

>>     the low side between 25-40 to on the high side between 150-200,

>>     mostly between 150-175.   Tech said that showed the expansion

>>     valve was working as the high would go up, low would go down,

>>     etc.  Then I revved it up to 3000-3500 rpms for a minute or so

>>     sitting there.  Looked at the pressures and noticed the high was

>>     now up around 200-250, but quickly would come down again.  He

>>     said this seemed odd for a R134a system.  He said maybe the

>>     expansion valve has a clog, or is sticking sometimes?  I did

>>     jumper pins 5 and 7 on the Klima relay and compressor spins just

>>     fine.  Something is causing it to stop spinning.  It is NOT the

>>     fan (high pressure switch on dryer) because that has been

>>     disconnected and hotwired to always run the secondary fan (I will

>>     be addressing that shortly).  Maybe the low pressure switch is

>>     bad on the dryer?  Maybe the expansion val ve is sticking?  

>>     Maybe the rpm/speed sensor on the compressor is bad?

>>      

>>     What I don't get is the inconsistency I see.  In park/idle it

>>     always seems to work and can't get it to stop.  Once I drive, it

>>     could be a few minutes or less, or 10-15 minutes, maybe even an

>>     hour until it stops.

>>      

>>     What else can I check or test?  Any ideas?

>>      

>>     Thanks in advance.

>>

>>     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

>>     ------------------------------------------------------------------------

>>

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>

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