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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21982
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Transporter: , I have a vw t5 2.5 tdi, PD. And suddenly it

Customer Question

Hi, I have a vw t5 2.5 tdi, PD. And suddenly it started to blow only cold air from the fan, doesn't matter if the switch is on cold position or hot. With cooling system everything ok, heating normal, no ower heatings. I was tacing apart front panel and everything looks ok.
Submitted: 1 year ago.
Category: UK Car
Expert:  Matt replied 1 year ago.
HelloVery first thing to do is ensure the coolant level is up to the mark and if low top it up with the correct antifreeze or pre-mixed coolant as stated in the owners manualI'd then check that the engine is getting up to temperature, if its not then its likely the thermostat needs changing.If this is OK have a feel of the two coolant pipes that pass into the car through the engine bay bulkhead, both should be warm with a warm engine. If they're not then its likely the heater matrix is blocked and you should do a reverse flush on the cooling system to try and clean it out. This is done by removing the top hose from the radiator and placing a garden hose into the engine water outlet, and then run the hose until you get clean water coming out of the radiator.If this doesn't help this only leaves checking out the motor / cable that moves the air mixing flap that allows the hot air from the matrix to enter the car air system. This flap is controlled by the temperature knob / dial etc and I think is controlled with a small motor for your car so the thing to do is first get access to the back of the control knob and measure the voltages is present there, then trace the wiring back into the dash from the control to locate the motor. It’s worth first checking the fuses for the fan / control circuit I'd recommend first removing the glovebox ( undo lower edge hinges from dash) to gain access to the dashboard inner and also allow you to shine a torch to the back of the central console so you can start tracing the wire back and see how things are put together
Customer: replied 1 year ago.
Well I can try to wash it at the weekend, but can explain little bit more, I add a image of Coolant circuit. So as you was telling me that both hows have to be hot, but instead it is an opposite. Looking at the image 1.Heat exchanger, the purple how should be less hot then red one, because it's coming out of the exchanger, but in my car that purple is HOT and red one the intake is COLD. And one more thing, that small how that comes back to the expansion tank from the heater, when I toke it of no coolant was coming from it, even when I was holding throttle for some time around 2000/3000 rpm. So firs idea was that the Nr. 15 Recirculation pump is not working, because this problem started just at once, not like the heater started to blow cooler and cooler air.
Expert:  Matt replied 1 year ago.
thanks for the extra informationI'd agree that its quite possible the heater pump isn't working especially if line 9 isn't flowing the pump should be on the side of the engine block so 1st check that its getting 12V and is running with the heater on hot and the ignition on
Expert:  Matt replied 1 year ago.
Hido you still need help?Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you