erainwater

Hi, Guys,

I have a '96 U.S.-spec C280 with the thermostatic climate control. When I put it in auto mode, it goes on maximum cool and stays there indefinitely even if the temperature control is cranked up to 92F. The A/C diagnostic mode shows that it does apparently recognize the internal temperature sensor, and gets an accurate reading. The only thing I've been able to determine that might be an issue is the fact that the outside ambient temperature sensor is showing "open". However, I was under the impression that this only had a slight effect upon the A/C operation.

Has anyone encountered this before? Thanks for any and all help.

leewater
'96 C280
'84 190D
'80 240D
'72 300SEL 4.5

scorchie

What about the other temperature sensors? If the cold air registers as being warm, it might blow cold even if you don't want it to.

I agree, the outside ambient temperature sensor has only a small effect on the automatic climate control. However, the heat exchanger temps and evaporator temps do make a difference.

-s-

erainwater

Good point. Unfortunately, I don't have the key to the remainder of the diagnostic codes in the A/C, so I don't really know what temperatures are what (other than that "01" is apparently the interior sensor temperature. I tried an internet search for the codes, but didn't find anything specific to the W202. Anyone know where I can find them?

Thanks again,
leewater

scorchie

Look at my recent posts, I just posted them within the last few days.

-s-

erainwater

Thanks, I found the codes.

My readings were as follows:
In-car temp: 96F
Heater core temp: 45F
Evap temp: 42F
Refrig. Temp: 89F
#9 (?) 51F
Blower Voltage (?) 240

The only think I found that seemed odd was the blower voltage. I'm hoping to narrow down the problem before I start swapping parts.

Do the W202's have a mini-blower that draws air across the interior temp sensor like the W201's? There doesn't seem to be any airflow into the sensor opening.

Thanks for your help.

erainwater

I might add that the system behaves the same regardless of the in-car temp reading. In the mornings, the reading is still in the upper 60's, but the system refuses to blow anything but refrigerated air unles the temperature is turned to MAX.

Jano

My A/C does not work whenever I am on full throttle for many seconds at a time; meaning cold air ceases to flow. Instead I get only warm temperature air. My guess is this happens when the car delegates it's power from the A/C so that the engine can work best when in full throttle -(pedal to the floor).

erainwater

I thought that I would post my findings in case they were of use to anyone else.

First, the car was apparently in a minor fender bender at some point, and the outside temperature sensor was never replaced when the front giblets were put back together. I replaced it for about 16 bucks plus shipping.

Secondly, the p.o.'s kid (or the p.o.) had stuck something up in the interior temperature sensor port (I know, because there were marks on the port from something having been shoved up in there...) and bent the thermistor up so that it was jamming the fan. A couple of minutes with the tweezers rectified the situation.

With both sensors now operational, the HVAC system works like a charm.

Cheers,
leewater

Rincewind

what happened to your c43 scorch

i want your wheels

blackmercedes

erainwater,

Your too cold AC problem is usually:

1. Bad monovalve, or

2. Bad evaporator temp sensor, or

3. Bad interior temp sensor.

It is probably the first one, and it's not an uncommon repair on W202 cars. Given your readings, I am pretty convinced that's the problem. Your ACC keeps the evaporator at the correct temp, and the monovalve regulates the temp of the air coming into the cabin. If it sticks in the "cold" position, then you get nothing but cold air.

Now, your interior reading of 96F could also be the problem. the car thinks it's durned hot inside and blows full on cold air.

I would begin by swapping out the interior temp sensor, as it's easy and inexpensive. If that does not solve the problem, then you're probably in for a monovalve replacement.

Rincewind

wow 140k 98 c230

mine just hit 60k and im getting it serviced soon

are you the orig owner? i was wondering if you could list all of the things that went wrong/bad while you had it

blackmercedes

Bought new Dec 1997. My first new MB.

At ~40K the valve cover gasket was replaced.

At ~80K the left axle seal started to sweat a teeny bit, so all three final drive seals were replaced.

At ~100K both lower front ball joints were replaced, showing VERY slight wear. Bad heater blower motor replaced then too. MUCH easier than previous chassis'!

At ~125K the shifter bushings were replaced.

The seat cushion MB Tex on the driver's side has worn through Instead of ordering a new seat bottom, I took the car to an upholstery shop and had it repaired. That was a few weeks ago.

No electrical failures.

No AC/ACC failures.

A long time back, when I was having the dealer do the servicing, they overfilled the crankcase by about three litres of oil and blew out both main seals. I don't "count" that, as it wasn't a manufacturing fault. They replaced them at their cost.

Overall, this is the best made car I've owned. Compared to our Honda/Acura ownership experiences, it's head and shoulders above.

However, we sold our 1998 E300 as it was a "hoist magnet" that could barely make it home from each trip to the dealer.

The C36 was very durable, but expensive to maintain. Not Porsche expensive, but AMG parts are $$. Thank goodness most of the car was run-of-the-mill C280! Also, tires cost us the GDP of some small nations thanks to the heavy right foot the AMG cries for.

Rincewind

wow nice... nothing too major