ac cutting in and out
 

i noticed the ac on my 90 350sdl was not working too well on a recent trip. my first thought was low freon. then i noticed that the car seemed to be missing out from time to time. finally i realized that the ac compressor was cutting in and out by the clutch.

so,... do they cut in and out if freon is low? or is is likely a problem with the clutch itself?

tom w

I would be suspicious of:

- Klima relay
- Bad wiring at or to the clutch
- Faulty ignition switch - this can cause you to lose a/c

Others will chime in with their opinions.

more detail
 

it will cut in and out every second or two.

tom w

there's a number of things that can cause this. one is a restriction downstream from the high pressure switch or a bad switch. The pressure goes up until the switch is opened, which causes the compressor to cut out, which causes the pressure to drop, which causes the pressure switch to make, which causes the compresor to engage again, which increases the pressure until the switch opens, etc, over and over.

I'm not an a/c guru, but that quick of a cycling rate sounds more like an elect. issue. - electrical as in a/c elect. circuit(s). I'd be suspicious of bad clutch wiring or elect. connection(s) at that point.

Just my 2 cents.

I can probably help you troubleshoot it, Tom, if the Klima sockets are the same as the '87.

As others have suggested, it can be a slew of different possibilities.........impossible to pin down without further tests.

well
 

i dont know what a klima socket is. but i would guess that they are the same as an 87.

tom w

There is a relay called the "Klima". It's about the size of a pack of cigarettes and is found between the firewalls in front of the driver. It just unplugs from the sockets.

thanks
 

brian, i am not going to try to fix it myself. i was just getting some ideas. about all we can do is shoot some freon into it. i was hoping everyone would say "just shoot some freon into it and everything will be cool". i suppose i will just break down and take it in. may be we'll shoot some freon into it anyway, first.

tom w

Tom, there are at least 10 good ideas. But, only one of them will be applicable to your vehicle. That's where troubleshooting comes in. It's not all that difficult to work through it and determine what the situation is. This is especially valuable with the electrical system, because many mechanics don't have a clue how to approach it.

I would have thought that you would take a more diligent engineering approach rather than the rather hopeless shotgun approach.

Nobody with any knowledge of these systems would ever tell you to "just shoot some freon into it and everything will be cool". You know better than that. ;)

brian
 

you are right. but i am too old to learn about something that i am not interested in. i only have so much time and energy and ac just doesnt interest me. shooting in some freon is easy and we have the stuff to do it. it doesnt seem too likely to work but we may try it any way just in case.

thanks for your attempt to help.

tom w

shoot refrigerant into a system that's properly charged and you'll now a system that "short cycles".

The pressure swicth will detect an over-supply of juice and cut the compressor off. the system will turn on-off more rapidly than it should and you'll get inadequte cooling.

more is not better when it comes to refrigerant.

just put the car in the shop

.........yes, I can sure sympathize. But, the a/c system is a bit complicated and, I'm in agreement with 300SEL. If you don't have the knowledge or the skills, just bring it to a qualified mechanic.

so
 

i dropped the sdl off at the ac shop this afternoon. i described what it was doing and he said.... get this... probly just low on freon!

heh heh. my luck if it is..oh well, if that is all it is it will still be a pretty cheap fix.

tom w

..........why am I not at all surprised.................. :rolleyes:

Hope you get lucky. ;)

well
 

it was just the first thing that he said without doing any actual diagnostic work. i just thought it was fun. i bet he says that to all the girls.

tom w

I know what is wrong with your car :cool:

Your auxilliary fan isn't working. The head pressure is skyrocketing and cycling the compressor off and on. You risk damaging a lot of expensive parts by running it in this condition. :eek:
The fan can be a ***** to replace. Get it fixed right away.

car is fixed
 

i havent picked it up yet but he said it was a loose wire on the... for got what .. the high pressure switch? maybe. anyway fixed and prob even cheaper than low freon. some one hit it on an earlier post.

tom w

picked
 

up car. ac working fine. $30.

tom w

You lucky SOB. Nobody fixes an a/c system for $30. :cool:

my friend
 

the machinist says i am the luckiest guy he knows. i dont always agree with him but a lot of the time i do.

tom w

I don't want to jinx you, but..........one of these days.......that machinist is going to hit the jackpot. :eek: :D

hope
 

he does. he is a good man.

tom w

I have a similar fellow who does all the smaller pieces for the jet engine tools.

Has been in business, working with his own two hands, for 35 years.

Can typically work to .0005 on a lathe. Then, of course, it is sent out to a proper grinding shop for finished size, and runout requirements.

He's made some beautiful parts over the years............but.........he's French Canadian...........so don't even attempt to tell him anything.............and............he's never wrong. :rolleyes:

ac cut out
 

again today. drove straight to the ac shop since i want the car for the weekend trip to the big Auburn Auction. they looked at the connections and said they were all apart and wondered why, then he looked at my serp belt and said wow that is coming apart. the pieces were flailing my ac connections apart! now i am wondering if this is why my tranny coolant lines were leaking.

do you all approve of the goodyear gatorback belt?

tom w

I do not know about the Goodyear belt. With MBs, I've always believed it's best to simply go OEM. Get one from a local MB dealer if time is an issue.

yes
 

i generally agree. my indie likes the gdyrs. hope it s ok as he is done and im going to pick it up.

tom w