Heater issue

[Danthomas]

I've researched this loads and can see the HCV is a common issue.. I've replaced this as I'm only getting hot air. However no change. Tested the new and old HCV by connecting 12v and can hear both clicking on and off.

I'm happy they're not the issue... Checked the voltage going to the HCV. Got the flowing results.

Dial set to hot - 13.7
Dial set to cold - 8.9
Middle setting.. . Fluctuates between the above two.

All interior electrics are working so assuming fuses are fine.

Why on earth am I seeing 8.9 volts on the cold setting. From what I've read it should be near 0.. Can't work it out???
Many thanks

 

[grogee]

So the next thing to try would be to disconnect HCV connector and see if your vent output is now cold.

If so I would suspect bad resistor in heater control panel, luckily they're cheap and easy to find 2nd hand (the whole panel with 3 knobs, I mean).

 

[Danthomas]

Thanks for your reply, I drove it around a bit with it disconnected and yeh it felt cooler but then I noticed steam coming out from under the bonnet. The coolant in the reservoir was bubbling and escaping Via the cap. I think you're right though and the panel is at fault

 

[grogee]

If coolant is escaping you may have a faulty degas tank cap. They are designed to keep the cooling system under a certain pressure. If they fail to maintain that pressure then the coolant is at or near atmospheric pressure and will boil at a lower temperature than it would at 'working' pressure. (Same principle in pressure cookers - water is at higher temp because of pressure and therefore cooks your food quicker).

Alternatively head gasket failure might pressurise coolant system and cause the cap to fail with these symptoms - were you checking it with engine running or engine off?

Alternatively coolant level too high. What was the temp gauge reading when the steam came from under the bonnet? On mine it's always been bang central no matter what I do, once its warmed up, which takes less than a minute most days.