Phoenix52

Hi everyone, the heater on my jeep is blowing cold. When I first start the engine and go on a half an hour journey from home it blows cold and does not get warm at all. When I do the same journey but before I leave home switch the engine on and then switch if off after a couple of minutes and switch it back on, after 10-15 minutes into the journey the heater blows warm and it works fine all day. Then I have the same problem the next morning if I don't switch the engine on and off before I go out.
The blend doors have been replaced in the last few months and they are working perfectly, there is enough coolant in the system, the temp gauge runs at 70
Could this be electronic ?

Hymie

The aircon (blend door position) is controlled by a pic controller – quite why Jeep thought it necessary to have a computer chip performing such a simple task is beyond me.

However, the system does allow you to interrogate the blend door setting/position (and ‘manually’ adjust their positions). To enter the diagnostic mode you have to press and hold a couple of the control buttons simultaneously. The aircon display will then show any fault codes and allow ‘manual’ control of each blend door (a set value between 0 and 255).

I can’t recall exactly how this is done – but if you search my posts (and others) on this site, you should find out how to enter diagnostic mode.