Heater output
I’m having trouble with the interior heaters in my 2014 SEAT Leon
1.6 TDI. With the dial on fully hot, on one day they are hot and on another they are lukewarm or cold. Similarly, sometimes the right vent will blow out warm air and the left vent will be cool. A couple of times I have had to top up the coolant slightly because the warning light came on telling me the coolant was low. It was slightly damp under the expansion bottle, so I fitted a new cap. Would it be worth trying a new coolant bottle, say if the threads were worn where the cap screws on and letting pressure out?
Looking under the car there are two auxiliary water pumps – one in front of the radiator and the other behind the engine, which seems to be plumbed to the EGR cooler. Would these have anything to do with supplying/pumping water to the heater matrix? Or do you have any other ideas?
Danny Clark
The heater unit in your Leon uses servo motors to operate the air flaps to direct air either through or around the heater matrix. The left and right sides of the heater unit have different flaps and this could cause one vent to blow warm and the other cold. I suspect the problem lies within the heater unit, not due to pressure loss in the main cooling system. As you do not mention any overheating problems with the vehicle, I believe the water pumps are operating correctly.
As you suspect, the EGR pump does supply coolant to the EGR cooler and the other unit is possibly a heat exchanger, which would indicate you have an auxiliary heater fitted, although, according to the data I have, this was not usually fitted to your vehicle. If there is an auxiliary heater, I would not expect you to have any heating issues, so it may be the case that it’s not operating and would need to be investigated further. It could be the unit that you identify as a pump at the front of the engine is actually the four-way thermostat, which is fitted behind the alternator.
Unfortunately, the heating control unit in your SEAT has no fault memory and there is no self-diagnosis function. I would begin by checking the operation of the flaps in the heater unit. By removing the glovebox, you should be able to gain access to the servo motors and ensure they are operating freely.