Mk4 Heater Control Valve diagnosis. Cold air only

[Tingana]

Hi, I have a mk4 Fiesta 2001 with a heater that only blows cold. Ive read many threads on various forums and will outline the steps I have taken so far:

Expansion tank level is at max. I ran the car with the HCV disconnected from the electric supply and no change, still cold. I took the expansion cap off and ran the engine while squeezing the pipes incase of air lock, no change. I read if it runs cold with electric supply to HCV cut off, then the HCV is at fault if no air lock. Is this true?

The two pipes going into the HCV from the engine are hot. The left pipe going out of the HCV into the dash area is hot, but the right side is cold. 

I want to make sure it is the HCV I need before I buy one. Thanks for any help

[Paulkp]

I think the HCV works on a variable mark/space square wave, not an analogue DC voltage.  Substitution is the easiest method of checking, unless you have access to a voltmeter to see if the mean voltage to the HCV varies as you adjust the heater control - Puma website may have some posts on the HCV

[Tingana]

Thanks for the reply. Ive bought a new HCV. Ive got a feeling its the thermostat now as I never see the radiator fan on. (no temp gauge) Top rad hose is hot and bottom is a lot cooler after driving. Going to check the matrix is ok now with a flush as I dont understand why hot is going in but the out pipe is cold.

I will keep this thread updated anyway as these posts help others when googling. (Nothing worse than reading a problem same as yours and the poster says they have fixed the problem and doesnt say how, or doesnt update at all) Id rather this hassle of diagnosing as I learn things and above all its free. 

[Tingana]

Good news, I have heat! As I took off the HCV, the hose going into the matrix just pulled off as the HCV outlet had disintegrated and crumbled away inside the hose.After clearing plastic debris from the hose I fitted new HCV and tried engine, no change. I then flushed the heater matrix which was at first blocked but with some shaking on the flushing hose it cleared and came out the other end. Flushed it backwards and forwards, refitted everything, ran engine for 1 minute with filler cap off to clear air and BINGO, gorgeous heat through the vent.

Job done.

[Paulkp]

Glad to see all fixed in time for the cold weather !

And thanks for posting the solution.