Q: My car dashboard only blows HOT air. What is the problem?
A: This is a common fault. We will explain what you need to look for:
The temperature of the air coming through the vents is controlled by the Air Conditioning Control Module. All S-Type’s have Digital Control as standard, allowing occupants of the front seats to choose the precise temperature required using the temperature control buttons next to the LCD display in the centre of the dashboard. When you choose the temperature required, a signal is sent to a part near to your vehicle radiator in the engine bay (this part is called the Dual Climate Control Valve or DCCV), which diverts the hot water from the engine cooling system into the dashboard, allowing the dashboard to blow hot air through the vents and into the cabin.
What can go wrong?
The common problem with the system described above is the failure of the DCCV. From this unit, two pipes go into the dashboard – one pipe for the Drivers side heating, and one pipe for the Passengers side heating. If one of the valves is worn it will “stick” open – causing an unwanted constant flow of HOT water into the cabin, rather than a “regulated” flow which would be needed to keep the temperature in the cabin at anything less than hot. Sometimes just one valve will stick, causing hot air on just one side of the cabin, and sometimes both valves can stick causing hot air on both sides of the cabin. It is VERY important to fix this issue as soon as possible, as further damage can be caused to the heating system if the DCCV is not repaired or changed. If you have to drive the vehicle, you can prevent further damage by turning the Heater Control System OFF.
What does the DCCV look like?
There are two types of DCCV, a 5-PIPE version and a 3-PIPE version.
The 5-pipe DCCV is fitted to all Diesel engine models, and Petrol models 1999-2002. For an example of this item see the following link S-Type 5-Pipe DCCV.
The 3-pipe DCCV is fitted to all Petrol models 2003-2007. For an example of this item see the following link S-Type 3-Pipe DCCV
I have replaced the DCCV but there is still a problem
If the DCCV has been faulty for some time, it may have caused an electrical overload to either the Air Conditioning Control Module or in the worst circumstance the wiring from the Air Conditioning Control Module to the DCCV.
The Air Conditioning Control Module can be replaced with a like-for-like unit. It is vital to match the part number on the new unit to that on the old unit. To find your part number, you will need to remove the Air Conditioning Control Module from the dashboard and look for a sticker with a long number which will have the format: ” ****18C612** “. You will need to note the variable numbers – i.e the four digits BEFORE the “18C612″ and the two digits AFTER.
NB – cars with built-in Touchscreen Sat Nav Screen will have a separate Air Conditioning Control Module. This is found inside the dashboard itself, above the glovebox internal housing (you will need to remove the glovebox door and internal moudling to reveal it. For an example of how this unit looks see the following link: S-Type Air Conditioning Control Module for Sat Nav Models)