Mercedes Sprinter recirculated heater/cabin air not working – Repair

For older Mercedes Sprinters (Pre-2006) without air conditioning, the recirculated air function is controlled by pressing the heater distribution rotary knob on the dashboard. This in turn lights a red light in the centre of the control knob to indicate recirculation is selected. Pushing the control again will turn it off.

This is a very simple system to troubleshoot and it should be possible to get it working or at least identify the problem quite quickly when you know where to look.

The recirculation system is controlled with a block off flap covering and limiting outside air from flowing into the cabin from the large fresh air intake under the bonnet. If the system is working correctly, once the dash switch is turned on – the flap should close and when the switch is turned off it should open. This physical movement in conjunction with the dash switch position can be easily confirmed by looking into the air box intake.

Heater recirculation control - Mercedes Sprinter 1

To the right of the air box, up top, is a vacuum controlled sprung actuator that pulls the flap closed when vacuum is applied to it. The vacuum origin is supplied from the ‘T’ piece connector on the brake servo vac pipe junction that also feeds the turbo actuator control valve. The brown hard vac pipe follows up along the top of the bulkhead from left to right terminating at the top spigot of the three port heater box flap control valve. The output from this electrically operated valve is the spigot facing the front. The final spigot at the rear of the valve had a small filter allowing pressure equalisation of the actuator when the valve is deactivated.

NOTE: It has been known that a failure of the recirculation flap actuator valve (venting to atmosphere) or leaking supply pipework has lead to turbo boost control issues. This is because the take off on the brake servo vacuum pipe is shared with that of the turbo control circuit. Any vacuum loss here and the turbo actuator will ultimately be starved of its controlling supply, causing underboss and poor performance. Always add this simple check to your turbo boost problem troubleshooting as it is often overlooked. Frequently the pipe is dislodged when the battery is removed/changed because of its location.

The recirculation flap control valve is fixed to the upper right hand side (UK Models) of the heater box above the battery. It can be removed by undoing a single cross head screw and pulling the unit sideways off a small support post/moulding on the side cheek of the ventilation air box. Electrically there is just one connection to the valve. A 12v supply is applied to the valve solenoid when recirculation is required, changing the state of the vacuum valve to allow suction to be diverted to the actuator closing the flap.

Heater recirculation control - Mercedes Sprinter 2

Diagnosis is simple, check that you have vacuum at the pipe feeding the valve, check voltage is present across the two terminals at the electrical connector plug when the dash recirc-switch is on. Rectify either of these faults. If all seems ok but there is no movement of the flap, then temporarily connect the supply and actuator pipe together – the actuator should retract and close the flap – if it does not the solenoid control valve is probably faulty and requires replacement. If vacuum is present at the output of the valve (the port that goes to the actuator) then make sure the flap mechanism is free. You can operate the flap manually by moving the lever at the side of the cabin air box above where the actuation valve sits. If you have no movement and the valve is providing vacuum to the actuator, check the rubber hose has not come of the actuator. If this proves to be OK the only logical remaining problem could be with the actuator itself, most likely holing of the internal diaphragm causing a leak. If this is the case the actuator will require replacement.

Once things are back together and working normally again, you will be able to hear an obvious change in the rushing sound of the air movement through the cabin air ducts when the dash control is activated to select recirculation on either medium and higher blower fan speeds.

10 thoughts on “Mercedes Sprinter recirculated heater/cabin air not working – Repair

  1. Hi Steve,
    I have a whine that gets loud and appears to come from the cabin air intake area. It’s loud in the cabin and louder when the passenger window is opened. It’s occurred twice now, both times at low speed. The first time it went before I could open the bonnet and the second time it I got the bonnet up and it appeared to be the air intake but again the whine went after a minute. Both times the heater was set to cold and the fan off as was the recirculation. The engine was warm. I would really appreciate any info. you can give me.
    Alan H.

      1. Thanks SteveSteve,
        The whine/screech is intermittent, and just occurred again. I think the noise is actually coming from the heater control valve mounted on the bulkhead below the intake. (it has two water hoses and an electric connection). When the ignition is turned on it sometimes makes a rapid clicking noise. There was slightly warm air coming into the cab this morning even though the heater was set to cold. I would imagine that a replacement part would be needed unless the valve could be easily serviced.

      2. Hi Alan,
        Give this a read and see if it helps. You can dismantle the valve on a 320CDI saloon and I assume you can do the same on your model. There is two mushroom valves inside and what happens is they either stick or the stem part breaks off leaving the top hat piece floating to block off the water flow to the heater
        Hope this helps
        All the best

  2. I have a 2004 Dodge Sprinter 2500. There is a particular fuse that keeps blowing, and it is linked to the honk/air recirculation solenoid valve. The first few times I replaced the fuse, I was using 25a fuses, as these were the fuses being used prior to me acquiring the sprinter from a friend. I noticed on the fuse diagram however, that a 15a fuse was required. I switched them out and went an entire day without any issues. The next day, the fuse went out once again. I notice it goes out when I go uphill or go against decent wind resistance. Anyway I can do a self repair on such? Any help would be great.



    1. Hi Haapai,
      Often the horn itself is the issue here, the body of the horn shorts onto the metalwork of the chassis taking out the fuse. See here for more detail and a diagram of what is connected to Fuse No.7 on the fuse board. Check out the horn and its connections first.
      All the best

  3. The issue you mention with the pipe being dislodged and affecting the boost causing loss or performance.
    My Sprinter did exactly that some time ago when the climate recirculation button was on. Much puzzlement.
    Checked it today after reading this & the hose was split where it pushes onto the valve.
    Cut the damaged bit off, reattached & normal service resumed!
    Many thanks!

  4. Hello, I would be most grateful for any thoughts on the following problem with my 2015 Sprinter 3500, which nobody from the dealer to the headquarters of Mercedes is able to answer.

    The manual says “Air-recirculation mode switches off automatically after about 10 to 30 minutes, depending on the outside temperature.”

    My Sprinter switches out of recirc mode without fail every 10 minutes. It is clearly not temperature-dependent as I have noticed this on long journeys at temperatures from the mid-teens (Fahrenheit) to the 60s. This is a critical issue for me due to my wife’s respiratory ailments, which are triggered by the more frequent than expected influx of exhaust fumes.

    The dealer has mentioned a “PSM” (some kind of programmable module) that either may be defective, or could be modified (but only upon authorization by Mercedes HQ). Needless to say I have not been given any hope of a quick solution.

    Do you have any thoughts?

    1. Hi Austin,
      It is normal behaviour for Mercedes recirc-mode not to be permanently maintained. The saloons I work on and also drive do exactly this. I suppose the idea is that the air inside the passenger cabin does not become stifled and without adequate ventilation (oxygen) causing drowsiness and possible accident. As far fetched as this sounds it is probably the main reason for its auto switching off. I would look to replacing the paper filter element in the ventilation box with an active charcoal filter that should do a better job of removing particulate and odours from the fresh drawn in air.

      Hope that helps

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