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.

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'81 300SD

I had an air cooled Karman Ghia , 40 hp, which I installed an AC into.. I put a normally ON switch by the left side of the shifter which was under my thumb... so from a stoplight while I was getting going.. I just held that switch down... it made a lot of difference... and my hand was right there for shifting anyway....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I was able to dust off the evaporator and apply some foam evaporator cleaner with a long, narrow brush. The system brought the vent temps close to 38* within 5 minutes with 79* ambient temp. I'm pretty happy with the system now, time to obsess on something else.

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'81 300SD

That is great news Otto....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

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
.

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'84 300D (211k) *New*... (Wife's)
'85 300TD (174K) 10th Year... (Mine)
'96 F-350 7.3L Dually (149K) Since New
'85 300D (156K) ~~~Wrecked~~~ Damn it! (parts)
'84 300D (176k) ~~~Wrecked~~~ Damn it! (parts)