shorthair

My 02 W203 C320 has a problem the dealer has been unable to diagnose. It started after the heater box was replaced (for the smell) a while ago.

The issue is that that with the A/C off and the temp set to LO when I drive the car, stop for say 20 minutes, then get back in an drive some more the ventilation blows hot air for about 10 minutes, then starts to cool down slightly. After about 15 minutes it is noticeably cooler, but still significantly hotter than ambient temperature. It is so hot I have drive with the windows open when it is 60 degrees out just to get cool air (or put on the A/C). And yes, I know that because the air intake is under the hood the air will always be a little warmer than ambient, but that is not my complaint.

It never used to do this before and the dealer is indicating this is normal behavior. They have checked the obvious things (fault codes, etc..) and did find an air flap that malfunctioned and replaced that, but it did not correct the problem.

Obviously something is calling for hot water to circulate when it should not be, and it does it for about 10 minutes and then starts to taper off.

Has anyone seen this before or maybe have ideas what should to be checked?

This is driving me nuts!

shorthair

Anyone?

Hightower

sounds like a fault with the flaps, there not closing and stopping air from passing over the heater matrix i think. your dealer should sort this out for u. otherwise complain complain complain!

CalifSLK

A/C control is a complex issue. There are a number of sensors that it uses: Ambient temperature sensor (in the nose), cabin temperature sensor (in the dash), sun load sensor (near the front edge of the windshield), and the evaporator core temperature sensor (in the blower box).

Since the original reason for replacing the blower box is unrelated to the current issue, it is likely related to the new blower box. If the core temperature sensor came with the new blower box, why don't you ask them to put the old one back in?

The premise is not necessarily that the new sensor is bad. It may just be a different version.

shorthair

They have already checked the flaps and did find one error and fixed it.

Unfortunately it is too late to put back in the old temperature sensor.

I was looking back over the records and I did have the instrument cluster replaced after the evaporator. They had to do some version coding because the gas guage did not work with the new cluster. Is there some version coding in the cluster related to internal temperature control?

CalifSLK

The interior temperature sensor is on the dash somewhere. Make sure it is not disconnected. It may have a positive flow tube to draw air thru the sensor.

There may be version coding for the temp sensors. For instance, the light sensor on the windshield has at least 3 code values. If there are, the master parts list would show all versions.

shorthair

Just an update: My car has been at the dealer since 9/18. Arrggh, but at least I have a nice loaner car. (This was not the only problem - it also died and wouldn't start and the drivers seat malfunctioned, plus a few others...)

As far as the ventilation goes, they continue to see intermittent faults from the diags so they will be ripping apart my dashboard yet again to replace the evaoprator for the 2nd time. (Which is fine by me as it is quite odoriferous again). The top mechanic said that the heater box seems to be out of spec which may be causing the faults. He also said that the hot air issue is normal for these cars, but will also check the operation after they are finished and compare to other similar cars. I told him I just want it to work the same way it did before they replaced the heater box the first time.

Sigh...........

CalifSLK

If it smells, it may just be a stopped up drain tube. Is the place you park your car level or at grade?

These cars are complex enough that it is never a good idea to tear into it with a seemingly minor issue. The dealer may or may not have the expertise to deal with the situation fully. Of course they never want you to think they can't do the job. Since technicians are human, the best guy may not be on your job that particular day.

Also, they get paid by MB to do warranty work. So it is not in their best interest to discourage a marginal replacement. The cars are assembled in sequential order, the dealer shop replacement may do things out of sequence and be a lot harder than when the parts was originally installed on the assembly line.

With so many problems happening to your car, one couldn't but wonder if they did damage the first time around.

shorthair

Thanks for the responses.

I park the car in the garage. It had been in the shop five times before they originally replaced the evaporator. The tube has not been clogged.

I agree. I agonized over this for several months, but the stink was too much for me so I agreed to let them replace the evaporator.

I just got the car back. They said heater box was physically distorted and needed to be replaced again as it was causing intermittant faults in various components. Who knows if they did that or it came in that way. They also replaced a bunch of other parts. The hot air problem is little better, but not like it used to be.

Well, it now starts, the drivers seat moves properly, it doesn't stink, there are no rattles in the dash, and they detailed the car - inside and out. I will keep my fingers crossed that nothing else goes wrong for a while.

CalifSLK

That's great. Hopefully it will stick.

In as much as the dealers claim that they are well trained, there are still variables in their skill level.