I have recently bought a 2006 mk1 2.0 crtdi. The heater wasn't working and the A/C is disconnected - compressor pump is not connected.. Have replaced the defective blower unit for the heater but it only blows cold air. The controls can be seen to be working the actuators, both direction and temperature, and the engine temp gauge is showing normal with the electric fan kicking in when stationary for awhile, so assuming the thermostat is ok. I'm assuming there must be a water blockage somewhere, but getting to the heater pipes is very tight and awkward, and there is a unit in the hot pipe line that I dont know the purpose for - feeling underneath it seems it probably has 3 electric connections - could it be a sensor ( for what?) or does it control water flow? Its the casting in the middle of the photo with the heater hot pipe going in and out.

Can anyone tell me what this is? I wondered whether to just bypass it with some pipe to see what happens....

 

Need to see more of where the lines come from and go to.

 

Looking from the front,(RHD car), the left hand pipe from the ali casting goes to the front timing belt end of the engine block. The right hand pipe goes down to the firewall and next to what I guess is the cool return pipe from the heater matrix. Not easy to get good photos -

 

I can certainly appreciate trying to get good pictures and it is not easy.

In the meantime , most heating systems have a coolant hose coming from the engine going to a heater core and another hose exiting the heater core going back to the engine. What we look for is , are both hoses getting hot after the engine warms up? That is the first thing we need to know. Can you check that and get back to us, thanks..

 

Well, took off the casting to find out what it was - it may be of interest to other owners in future. Having dismantled it, it appears to be an electrical water heater. The car has a switch to heat the front windscreen which confused me as there were no apparent heating wires on the windscreen - so at a guess the switch energises the water heater maybe just when the control is set to windscreen demister vent when the engine is cold.
Without a lot of dismantling it is not possible to get to the heater return pipe with the 2.0 crdi, there's just no room, so connected the hot heater feed pipe to an oil suction pump and pumped water back and forward ( with coolant cap off), to try to make sure there was no blockage. Replaced the casting with a short length of copper pipe as the unit was damaged dismantling it.
Now have a heater just in time for winter - not maybe as hot as it could be - but it is now warm air blown out!

 

You did a better job than some mechanics, nice going !!

 

Photos of its innards - never seen anything like it!