aircon blowing hot on driver side, thermotronic 4 zone

[ckember]

I Know there are several reports of many models having seen this fault over the years, where the drivers side blows hot or warm air and doesn't cool down. I have now had two duovalves replaced under warranty, the second as the first was replaced under warranty and now the warranty has expired, but now the dealer says the Actuator motor is faulty and needs replacing, how does this affect the airflow, where is it located and is £1300 for the part and 8 hours labour reasonable. What would a good Indy charge for this to be replaced? The dealer are looking into some goodwill towards the bill.

 

[ckember]

So after agreeing to goodwill at 51% and booking the car in, the dealers have had it for 5 days and still can't fix the drivers side blowing hot and the rest of the car cold. It wasn't the stepper motor or the control unit behind the dash, they are currently looking at the heater box, but can't find any messages in STAR

 

[Diesel Benz]

You do not have duo-valves on a CLS, you have one heat exchanger shuttoff motor/valve that controls hot water circulation. This valve is common for both sides of the car and only operates at certain extreme conditions. Most of the time the valve is fully open and cabin temperature is controlled by air flow flaps.

A new heat exchanger valve costs 30.06 Euros (current German price list).

The valve motor fails often, sometimes the driver circuit at the front SAM too but these would not make one side of the car hot/cold.

There is no Star fault code if an actuator motor runs fine from one end to the other but if the mechanism is broken and the flap makes no movement. I have no idea about the problem in this car but an experienced workshop can do much more than read fault codes from the diagnosis tool.

 

[Howard]

On my cls , My drivers side centre vent doesn't blow cold either.

The icy cold air comes out of the centre passenger side only.

 

[ckember]

You do not have duo-valves on a CLS, you have one heat exchanger shuttoff motor/valve that controls hot water circulation. This valve is common for both sides of the car and only operates at certain extreme conditions. Most of the time the valve is fully open and cabin temperature is controlled by air flow flaps. A new heat exchanger valve costs 30.06 Euros (current German price list). The valve motor fails often, sometimes the driver circuit at the front SAM too but these would not make one side of the car hot/cold. There is no Star fault code if an actuator motor runs fine from one end to the other but if the mechanism is broken and the flap makes no movement. I have no idea about the problem in this car but an experienced workshop can do much more than read fault codes from the diagnosis tool.

So what valve did they replace in September? That sits on the drivers side bulkhead near the brake master cylinder, under the bonnet, they called it a duo valve at the dealer and on the receipt! I did some digging around other forums and the expansion valve or the heat exchanger is a possible cause too. With 11 motors behind the dash it could be any from the reports I found. I agree any mechanical problem won't show in star. The is also a slight hiss which apparently could again point at the expansion valve. This is the problem with modern mechanics. If it doesn't have a sensor on it the engineers are not trained in good old fashioned trouble shooting. Good job the dealer is getting the parts on fix or return basis. I would be down nearly a grand already for parts I didn't need

 

[ckember]

So another day, and still no fix for the aircon issues, how in this modern world can it take 7 days and not have any idea what the problem is?

 

[Diesel Benz]

So what valve did they replace in September? That sits on the drivers side bulkhead near the brake master cylinder, under the bonnet, they called it a duo valve at the dealer and on the receipt! I did some digging around other forums and the expansion valve or the heat exchanger is a possible cause too. With 11 motors behind the dash it could be any from the reports I found. I agree any mechanical problem won't show in star. The is also a slight hiss which apparently could again point at the expansion valve. This is the problem with modern mechanics. If it doesn't have a sensor on it the engineers are not trained in good old fashioned trouble shooting. Good job the dealer is getting the parts on fix or return basis. I would be down nearly a grand already for parts I didn't need

The expansion valve is for the AC system. They probably did change the "heat exchanger shutoff motor", which is a valve but nothing like the duo-valves on older MBs where the valves actually controlled the HVAC heating power too.

Here a write-up for changing the valve on a LHD car:
DIY: Installing a new Changeover/Heater Control Valve - MBWorld.org Forums

Both valves (heating and AC) are common for both sides. Odd if nobody has experience about heating/cooling issues on once side (other than flaps which you should have been good).

Evaporator freezing at low refrigerant may cause hot air at one side but it only happens after a decent ride at humid conditions.

 

[h17n dj]

I have a thermotronic unit if you require?

 

[ckember]

I have a thermotronic unit if you require?

still waiting for the dealer to tell me what they are doing!

 

[h17n dj]

still waiting for the dealer to tell me what they are doing!

Good Luck!

If you require it, let me know and we shall work out a deal for it. Its in good condition and quad zone thermotronic unit

 

[Auto-mobile]

Usually the duo valve under the brake servo, I'd be suprised if it failed again after having 2 replaced in such a short time, but you never no.

There are also software upgrades for this problem, more so on w221

 

[ckember]

Finally all resolved, was the stepper motor, as they had previously thought, but had to use trial and error to find the right one. So after 7 days it's all working as it should. Just goes to show that good old fashioned logic can work if your ignore the diagnostic software and go with your gut. Having some help from the forum and having a little understand from the WIS, helped me point the dealer to keep trying the motors. Final price was £650, as I got 51% goodwill and also a further 6% discount.

The use of a 2015 facelift c250 premium plus estate for the 7 days was nice too!

 

[ckember]

Aargh, the only hot day so far and the same problem as last year has come back.

Warmer air coming out of the front and rear vents on the drivers side. Passenger side is noticeably colder, even think the flow is lower too. Takes ages to cool down even on recirculating mode. Also the ac has a whistle as before which seems worse when cornering. Also comes from behind the dash

Going to call MB when back from work trip next weekend. But any suggestions would help on the problem lease. Really don't want the dash out again.

 

[ckember]

Problem found to be a cracked condenser unit, will test when pickup the car tomorrow from the dealer. Hope the front bumper went back on ok