ac cutting in and out - PeachParts Mercedes-Benz Forum

t walgamuth · #1 08-16-2005, 11:05 AM

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

1991300SEL · #2 08-16-2005, 11:24 AM

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.

t walgamuth · #3 08-16-2005, 11:59 AM

it will cut in and out every second or two.

tom w

Pete Burton · #4 08-16-2005, 12:06 PM

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.

1991300SEL · #5 08-16-2005, 12:10 PM

Quote:

Originally Posted by t walgamuth

it will cut in and out every second or two.

tom w

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.

Brian Carlton · #6 08-16-2005, 06:02 PM

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.

t walgamuth · #7 08-17-2005, 12:09 AM

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

tom w

Brian Carlton · #8 08-17-2005, 11:56 PM

Quote:

Originally Posted by t walgamuth

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.

t walgamuth · #9 08-18-2005, 12:19 AM

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

Brian Carlton · #10 08-18-2005, 12:50 AM

Quote:

Originally Posted by t walgamuth

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.

t walgamuth · #11 08-18-2005, 08:20 AM

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

1991300SEL · #12 08-18-2005, 08:52 AM

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

Brian Carlton · #13 08-18-2005, 08:58 AM

Quote:

Originally Posted by t walgamuth

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

.........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.

t walgamuth · #14 08-18-2005, 07:32 PM

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