It reads to me more as a duovalve problem.

 

Thanks Skylaw, now researching Duo Valves. Had never heard of them before.

G.

 

The Duo Valve has three components: two solenoid-operated, computer-controlled coolant flow control valves, and one 12-volt electric coolant pump.

The flow control valves control the temperature of the left and right heat exchangers (heater cores). When the valve is unpowered, it is open and the heater core gets hot, and then so does the air from the vent on that side of the dash. When power is applied to the solenoid, the valve closes, and the air will be cold.

It is possible to remove the Duo Valve and check and clean it, which has a fair chance of fixing the problem.

To access the Duo Valve (as usual, these directions are for LHD cars):
- Lift the hood.
- Remove both wiper arms - pull off plastic caps, use 15mm tool. Remove and don't lose the small plastic rings found on each of the wiper studs. If the stud closest to the center of the windshield turns freely with the nut, use an Allen wrench (hex) in the end of the stud to hold it.
- Lift hood to the vertical position. Pull down slightly, push the small square metal arm on the driver's hood hinge, and lift the hood more vertical. Go to the passenger side, push the square on that hinge, lift the hood fully vertical. It is now safely locked in place.
- Find the four plastic Phillips screws holding the front edge of the black plastic rain shield at the back of the engine compartment. Back the screw almost all the way out, and gently pry/pull out the round plastic rivet that the screws were holding. Don't drop them, or the slip on nutplates that they screw into - they are plastic, and difficult to retrieve.
- Carefully remove the rain shield. It will be held in place by a ridge near the back of the shield that snaps into a groove at the base of the windshield. If you have the plastic wedge/pry bar tools, you can use those to go up under the lower edge of the shield and up to the windshield near one end. Pull up on the upper edge and pry up between the shield and windshield. Be very careful if you use metal tools to avoid hitting or pressing hard on the windshield! Work the end out of the rubber piece on the fender edge and carefully pull up along the top edge to snap the shield out of the windshield groove.
- Unplug the wiper electrical connector.
- Use a 24mm socket to remove the four nuts and one washer holding the wiper assembly, and lift it out. Try to avoid hitting the windshield, and also avoid turning the horizontal tooth wheel under the wiper assembly. This is adjustable to hold the front of the assembly in the proper position.
- Pull the rubber seal off that runs across the engine compartment.
- Use an 8mm tool to remove the two small screws at each end of the central removable section of the forward firewall. Either cut the wire ties holding the wire harness to the removable piece, or pry the metal rings from the ends of the brackets holding the wire ties, so that you can pull the removable section out.
- You now have good access to the Duo Valve. Unplug both power connectors. Pull the four hoses up as you firmly slide the Duo Valve toward the passenger side (to the left, which is toward the right side of the car). The rubber supports/retainers should slide out of the slots in the mounting plate. You can now squeeze and move the hose clamps down the hoses away from the valve on all four hoses. It is imperative that you clearly mark the hoses so that you can put them back in the same places! If you screw this up, you will have serious problems getting it right later! Remove the hoses - there will be very little coolant loss.
Carefully remove the five screws holding the solenoids down. Pull the solenoids off, being very careful to avoid losing the tiny springs on each valve stem. Pull the rubber seal off, and clean and check everything. Clean all corrosion and crud off of the valves and stems. Put everything back together, being certain that the tiny springs are in place.
Critical method! Lubricate the small screws before putting them in. When you start the screws, hold them down and turn them counter-clockwise (loosening direction) while carefully feeling for the screw to drop slightly. Stop instantly, and carefully snug the screw in a clockwise direction. This starts the screw back into the same threads where they were originally. If you do not do this, you stand a high probability of breaking the little screws!
- After the valves and solenoids are all reassembled, you can test them by applying 12 volts DC to the center pin of the connector, and ground to each outer pin (one at a time). With a solenoid powered, try blowing thru the hose connector - it should be blocked. Remove power, and it should be open. Check this several times for each solenoid valve.
- Remove the pump motor. Try rotating the round cup on the pump end of the motor to make certain that the motor moves freely. Test the motor by applying 12 volts DC to the connector pins - the one on the flat side is positive.
- Clean out any leaves, mouse nests, and other trash while you have access.
- Reverse the above steps, making certain that the hoses go back onto the same places where they were removed! You will have a little difficulty getting all three of the rubber supports to slide into the slots correctly - keep trying...
- If you removed the metal rings from the wire harness supports, use a socket that fits them to help push them back on.
- Don't forget to plug the wipers back in.
- The upper end of the rain shield will snap into the groove with hand pressure.
- Lower the hood to the normal lifted position before installing the wiper arms. Press the metal squares to release the hinges.
- Don't forget to install the small plastic rings on the studs. On left-hand drive cars, there is a small line on the right (passenger) side of the windshield that shows the position of the parked wiper arm. Loosely install both parts of the arm to the studs, then move the arm to the proper position by letting it rotate on the center wiper stud. This will take several tries. The left blade goes parallel with the right blade.
- Check and correct the coolant level, and repeat a couple of times over the next few trips.

 

I nominate this for the W220 S-Class Encyclopedia! Thanks, Wally

 

Hi,

2nd'ed, and done :wink

Cheers Dave