m103 W201 A/C trouble - PeachParts Mercedes-Benz Forum

d.delano · #1 08-17-2010, 01:18 PM

All-
Can anyone tell me where the evap temp sensor is located in the W201 w/ the m103? I'm having an intermittent issue where the A/C blows cold for some time after startup and during operation, then the cold air stops and it cuts out to just fan. Shutting the engine off then starting up again, the cycle repeats itself. I'm wondering if this sensor could be at fault, or something else? I have checked the refrigerant, the pressure at the low side is good.

tjts1 · #2 08-17-2010, 04:52 PM

I think its unlikely. The pressure switch is located behind the driver's side headlight. Its red with 2 wires coming out of it. If you remove the pressure switch you'll have to get the whole system recharged again. How hot is your engine when this happens? The system is designed to shut off the AC if the coolant temp gets over 115c.
good luck
Justin

Gilly · #3 08-17-2010, 05:08 PM

"I could be wrong" but I don't think there is an evap temp sensor, I think this older car has a capillary tube that runs from the evap to the expansion valve and that sort of runs the whole show.

What I would tend to lean towards is the "Klima" relay being bad. This is next to the fuel pump relay and looks just about like it, but has the word "Klima" (German for "climate" I guess) on top. Just for trivia's sake, the fuel pump relay lists the cut-out rpm and the number of cylinders (abbreviated as "zyl") on it.
Anywhoo, the klima relays main job to to make the ac clutch to engage. It takes in a few different bits of information and tells the ac clutch to engage or disengage. If the system is working normally, it might be the relay itself, or a popular failure would invlolve the engine rpm info or ac compressor speed sensor being bad, as the relay looks at engine rpm vs compressor rpm info and uses this info to detect a slipping ac belt. BTW make sure the belt isn't slipping! Or the AC will cut out, heh heh.
Gilly

d.delano · #4 08-17-2010, 06:57 PM

well I found this
http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1993@@1993&makeid=63@@MERCEDES+BENZ@@X&modelid=6132%3AED%7C10000011%3ASM%7C847%3AMBC%7C1486@@190E+2%2E6&catid=242213@@Climate+Control&subcatid=242253@@A%2FC+Evap+Temp+Sensor&mode=PD

but your Klima suggestion is compelling; how to test it to find out if it's the culprit?

Gilly · #5 08-18-2010, 07:55 AM

Well, I said I could be wrong. I have no idea where that would be other than plugged in to the evaporator case somewhere, obviously. I'm sure it would be accessable, just need to know where to look. Only think that really sort of troubles me is what the connector would plug in to?? Hmmm, I don't think there is a control unit? There is a control PANEL but I think that's just a bunch of switches, not a module per se. Weird.

The Klima has the power in and power out that could be jumped which would keep the clutch engaged all the time, so that would eliminate the clutch and wiring to the clutch as the cause, but not neccesarily tell you the Klima relay is bad, not to any reliable degree.
What you need is to find the electrical diagnostic routine for the AC system, I know it exists but not sure where you'd find it. MB shop or maybe that startek system (online).
Gilly

Gilly · #6 08-18-2010, 07:59 AM

As an aside, I would put a higher probablity on the Klima relay, as I have repaired cars with bad Klima relays, over this evap temp sensor that must be like a really really reliable part if I don't even know where it is!
Other possiblity is the compressor itself (bad rpm sensor), of course it could be some ratty wiring as well.
Gilly

d.delano · #7 08-18-2010, 10:03 AM

OK thank you for the insight. The temp sensor does seem like just a meat thermometer and those never seem to go bad.

Gilly · #8 08-18-2010, 01:14 PM

On the little bit later cars, they DO have probs, or at least did in the earlier production cars, with the evap temp sensor. Immediately what comes to mind are the first 3 years of the 210 chassis and the early w220 S Class cars. The engineers said they (the evap sensors) couldn't take the moisture, and the design was changed. But this was when AC was getting changed to electronic controls. The 124, 201, for example was a more basic system. It was an automatic system, but not really "electronic" like we think of it today.
Gilly

david s poole · #9 08-18-2010, 02:44 PM

the fact that the comp shuts down and won't restart until you cycle the ignition key smells of the speed sensor on the compressor OR the klima relay that it sends the a/c signal to.

johnflight1 · #10 08-18-2010, 04:52 PM

I am having the exact same problem on my 124 1988 300E.Gauges show a good charge. I am just driving along and the A/C cuts out and blower keeps going. Cycle the ignition switch and it comes back on. Now as it gets hotter here in vegas the ignition switch trick has stopped working!!
This is not a luxury here...... I will be watching this post carefully to see how it goes. Meanwhile I will be on my way to pick a part to grab all the ac stuff I can out of there 124's since that klima relay is over $100 bucks.................John

Gilly · #11 08-19-2010, 07:57 AM

Just wanted to point out again the info that I think the relay takes in; it's the only way the compressor gets engaged or disengaged, so it is taking in info from the high and low pressure switches, and also what David and I both mentioned, it takes in the engine rpm AND the speed signal from the AC compressor and compares them to detect AC clutch slippage and will cut out the compressor if it detects slippage. So obviously you want to be sure the belt is not slipping, make sure the belt is tight and in good shape, because under extreme heat conditions, that compressor is working pretty hard and makes the likelyhood of slipping more probable.
Gilly

david s poole · #12 08-19-2010, 01:23 PM

as a temporary fix until the weather cools down,take out the klima relay and find the two pins next to each other on the same side numbered 87&15.strip insulation off 1 1/2 inch stranded wire and wind it around the two pins.this will bring on compressor all the time that ignition is on and will not allow comp to cycle but in these temps that might be a good thing unless on a long trip.

Gilly · #13 08-19-2010, 08:49 PM

I believe the clutch would be engaged even with the key off. Same with a fuel pump relay, if you jump it, the car will run but will also run with the key off. Many will say it's a real bad idea to jump the fuel pump relay as the pump will still be running if you got in a bad accident, it could be very nasty in case of an underhood fire.

david s poole · #14 08-20-2010, 02:06 PM

no Gilly the clutch will not be engaged with key off as that is terminal 15 NOT 30 .terminal 15 is only alive with key on.if you remember on the fuel pump relay terminal 30 is used and that goes straight to battery positive.

Gilly · #15 08-20-2010, 05:43 PM

OK, wasn't sure.
Gilly