A/C clutch not engaging - PeachParts Mercedes-Benz Forum

pilot53 · #1 10-02-2016, 07:34 PM

I just finished overhauling the a/c system on my 85 300d, new evaporator, sanden kit, receiver drier, txv, low pressure switch, and temperature switch. The system is charged, but the only way I can get the a/c compressor to engage is if I jump the klima relay. Ive tried a brand new relay and that did not fix the problem, what else can I try?

leathermang · #2 10-02-2016, 09:45 PM

Recheck to make sure you have refrigerant... or that low pressure switch will be keeping the clutch from engaging...
Check all the wires which you have moved ... see if they have good connections.

pilot53 · #3 10-02-2016, 10:33 PM

jumping the low pressure switch doesnt turn on the ac. only jumping the klima relay makes it work, and it blows cold. so far ive checked the pushbutton unit, etr, klima relay, ovp, and the temp switch

funola · #4 10-02-2016, 10:41 PM

Klima relay needs a good tach signal.

pilot53 · #5 10-02-2016, 10:55 PM

My tach is working on the dash, is it possible to have a bad tach signal to the klima but a good signal to the dash?

funola · #6 10-02-2016, 11:04 PM

I maybe confusing it with W124 then. There is a micro switch on top of valve cover for compressor cutout during full throttle. Google for a klima diagram for w123

pilot53 · #7 10-03-2016, 01:16 AM

thanks, i figured it out, im stupid, had the pressure switch and temp switch on the r/d wires mixmatched...

leathermang · #8 10-03-2016, 10:20 AM

Quote:

Originally Posted by pilot53

thanks, i figured it out, im stupid, had the pressure switch and temp switch on the r/d wires mixmatched...

Like I said.... check all the wires you moved...LOL

funola · #9 10-03-2016, 10:37 AM

That was easy! I'd like to hear about the performance of your Klima Sanden kit.

pilot53 · #10 10-05-2016, 06:11 PM

Quote:

Originally Posted by funola

That was easy! I'd like to hear about the performance of your Klima Sanden kit.

Well it doesnt look like we will be getting any more hot weather in southeast NY state, but its been in the low 70s here and the a/c has been blowing ice cold on max. I would expect better performance with the sanden kit vs the r4 though. The conversion was not that hard, but obviously more involved than just changing the compressor, I did not have to hack away at anything or modify the kit in any way to make it fit the car, and the instructions was very thorough. It costs about $400 more than it would have cost to buy the tools and parts to rebuild and reseal the r4, or to replace the r4 with a new unit. But the car is for my dad and he plans on keeping it for a while so the investment was worth it, its a much better compressor than the r4 and we wont have to worry about future a/c system issues.

funola · #11 10-06-2016, 09:44 AM

Quote:

Originally Posted by pilot53

Well it doesnt look like we will be getting any more hot weather in southeast NY state, but its been in the low 70s here and the a/c has been blowing ice cold on max. I would expect better performance with the sanden kit vs the r4 though. The conversion was not that hard, but obviously more involved than just changing the compressor, I did not have to hack away at anything or modify the kit in any way to make it fit the car, and the instructions was very thorough. It costs about $400 more than it would have cost to buy the tools and parts to rebuild and reseal the r4, or to replace the r4 with a new unit. But the car is for my dad and he plans on keeping it for a while so the investment was worth it, its a much better compressor than the r4 and we wont have to worry about future a/c system issues.

The R4 reseal kit was $34. The clutch puller can be rented for free at Autozone. You can easily improvise the tool to r&r the R4 case.

Did you replace all the hoses or just the ones needed for the Sanden? Did you replace the condenser? What was the total cost? An unknown: how durable will the Klima Sanden kit be?

Demothen · #12 10-06-2016, 09:53 AM

Assuming that pilot53 used the same kit as I did and bought the compressor from as an addition to the kit, the compressor is an actual Sanden brand compressor, not a Sanden-style like I've seenaround. I can't speak to reliability obviously yet, but my understanding is the entire purpose of going that route is to improve durability over the R4. One thing I've noticed now that mine's charged is that there is very little drag on the engine. When my R4 was "working" there was a very noticeable drop in power when the compressor was engaged. Now I can hear the RPM drop slightly at idle, but while driving around don't even notice it.

funola · #13 10-06-2016, 10:12 AM

I do not notice any drag or drop in power with my R4 with 3 different refrigerants that I've tried: R134a R152 and R12. Maybe there was something not right with your R4 system? It did eventually grenade on you.

As for reliability of the R4's in 30 year old W123's, they need service just like your engine. Correct amount of oil needs to be inside and it needs to be clean and not moisture laden, seals need to be replaced. I am sure many R4's fail due to neglect, and is blamed on it's reliability. Sure the Sanden is a more modern compressor and maybe a little more efficient. IMO, if the R4 is properly maintained, it should provide good performance and many years of reliable service.

Demothen · #14 10-06-2016, 10:29 AM

Very true about the power drop, I am comparing apples to orangutans here, since I never had a properly working system until now.

I wish I could remember more about my grandparents' 240D, they lived in the deep south and it seemed like every other summer it was in the shop for AC work when I was visiting. I do remember it blowing foam insulation out the vents sometimes