Heater issues

[Nissan Dane]

2007 d40 2.5L

Getting to that time of year where the heater is a comfort i enjoy. I've read a lot of different theories but looking for someone who may have experienced it and fixed it.

At the moment if i am driving down the highway and i turn the dial to hot the cabin will fill with hot air. I can turn the fan on as well and it pumps out hot air. But as soon as i pull up at the lights the fan is still pumping but the air goes cold. All i have done at this stage is given the heater core a bit of a blast, but wondering if it might need replacing or is it the heater fan resistor? Any ideas would be great. Thanks

 

[red hilux]

Fan resistor is for the fan only. If that’s broken, potentially is only that fan speed that won’t work. try turning the fan on while stationary and see if you can feel and hear the fan speed changing. Of your feeling the air while driving and not stationary, most likely your on fresh air setting

 

[dno67]

Most modern vehicles use vacuum to control the heater switches, possibly a vacuum leak. Vehicle at low speed, low vac, higher revs more vac.

 

[typhoeus]

heater hoses good? are they connected the correct way ? Is there air trapped in the cooling system? If the fan is working, then its not the resistor, The heat comes from the coolant, so if it goes cold, the water flow thru the heater core has stopped. When the motor is at idle, the water pressure is low, and may not be enough to pump past a kink in a hose, or an air bubble in the system. Or if the hoses are connected incorrectly, its trying to pump to a high pressure area instead of to a low(er) pressure area of the system

 

[Nissan Dane]

After this mornings run, the fan speed is the same regardless of car speed, you can hear the difference between 1,2,3 full even if stationary. I think it will be coming down to the hoses and heater core. Judging by the way the driving lights and bars were wired, it would not surprise me if there is something going on.

I might start with inspection of all hoses. You say some can be on the wrong way? I did not realise that!

Thanks so far guys

 

[Belfy82]

Sounds like heater core needs bleeding to me. 70 series LC will do the same unless core bleed. It works while driving because water pump pumping some water to core at higher rpm. However when idle pump pressure not enough to force water through core.

When U say U blasted core did that involve hoses/core being removed?

 

[Nissan Dane]

Just update this. I did 2 things to get heater working. Used this radiator flush gun both ways into heater core pipes on firewall https://www.supercheapauto.com.au/p/toolpro-toolpro-radiator-flush-gun/573217.html with some spare clear piping and clamps.
Then to make sure no air bubbles in core, or any other part i used this https://sydneytools.com.au/product/daytona-drecoo-cooling-system-refill-kit-and-vacuum-purge.
Heater pumps like new again, I know I will be using purge tool to fill coolant whenever I swap now.