aclassdriver
New Member
- Joined
- Nov 20, 2012
- Messages
- 8
- Reaction score
- 0
- Location
- Leicestershire, UK
- Your Mercedes
- A Class / 2011 / 180CDI
I'm having trouble with the heating system. It seems way too sensitive.
I bought the car in March and reported the problem to the dealer, who took a look and said they couldn't find anything wrong. The problem went away during the summer (didn't need the heater), but has now returned as follows.
If the car is driven away from a cold start, with the cabin temperature control set to 20 deg C with the fan on low (1), the following happens.
After about ½ mile the heating system starts pumping very hot air into the car.
This continues for the next 4-5 miles until the cabin is very warm. Then, suddenly, the system starts pumping cold air into the car. Then after a mile or so more the system settles down.
If I set the control at say 18 when setting off, pretty much the same thing happens, although it settles down after a shorter distance.
In engineering terms the heating control system appears to have far too much “gain”. Even after the system has settled down, turning the temperature control up or down by just 1 degree can cause the temperature of the air coming into the cabin to change significantly (from cold to hot or vice versa).
I believe the car has a cabin air temperature sensor in the courtesy lamp housing and that the heating system is trying to control the air coming into the cabin so that the cabin reaches temperature in a timely fashion, but it seems to be far too aggressive. If the cabin temperature is only a little bit too low, then the system pumps in very hot air, and vice versa. The motorised flap controlling the mixing of hot and cold air coming into the car seems to be over-reacting.
The only way to warm the car up comfortably in winter is to set the temperature control to the minimum (i.e. Off) when setting off. Then slowly over the next 5-10 miles turn the control up in 1 deg steps.
I also notice the car windscreen sometimes suddenly mists up (even in dry weather) if I don't run with the AC on.
Is this normal for the heating control system on a Mercedes A class?
If it’s not normal, are you able to suggest what I ask the dealer to adjust/check/replace?
I bought the car in March and reported the problem to the dealer, who took a look and said they couldn't find anything wrong. The problem went away during the summer (didn't need the heater), but has now returned as follows.
If the car is driven away from a cold start, with the cabin temperature control set to 20 deg C with the fan on low (1), the following happens.
After about ½ mile the heating system starts pumping very hot air into the car.
This continues for the next 4-5 miles until the cabin is very warm. Then, suddenly, the system starts pumping cold air into the car. Then after a mile or so more the system settles down.
If I set the control at say 18 when setting off, pretty much the same thing happens, although it settles down after a shorter distance.
In engineering terms the heating control system appears to have far too much “gain”. Even after the system has settled down, turning the temperature control up or down by just 1 degree can cause the temperature of the air coming into the cabin to change significantly (from cold to hot or vice versa).
I believe the car has a cabin air temperature sensor in the courtesy lamp housing and that the heating system is trying to control the air coming into the cabin so that the cabin reaches temperature in a timely fashion, but it seems to be far too aggressive. If the cabin temperature is only a little bit too low, then the system pumps in very hot air, and vice versa. The motorised flap controlling the mixing of hot and cold air coming into the car seems to be over-reacting.
The only way to warm the car up comfortably in winter is to set the temperature control to the minimum (i.e. Off) when setting off. Then slowly over the next 5-10 miles turn the control up in 1 deg steps.
I also notice the car windscreen sometimes suddenly mists up (even in dry weather) if I don't run with the AC on.
Is this normal for the heating control system on a Mercedes A class?
If it’s not normal, are you able to suggest what I ask the dealer to adjust/check/replace?