Hi there,

I'm looking for a solution, my XJ-SC is blowing cold!
It seems to be hot when turning on but it quickly get back to cold after a few minutes. Air-conditioning is working properly.

Any idea?
Thx.
Yt

 

the "hot" could be the first bit of air in and around your hot engine and the rest just fresh air. This is just a guess, but check to see if the linkage on your heater control valve actually operates.

mine doesn't and just blows freezing air at me

 

Excellent, where can I find this linkage?

 

There is a vacuum switch that often gets stuck. It is up on the firewall. Has heater hoses and a small vacuum line. There a replacements easily available, if that is the problem.

 

On the heater valve itself. It is vacuum operated with an external linkage.

With the engine have a helper turn the temp control from extreme to the other. You actually see the linkage operate.

If it doesn't move it's either broken/stuck, or it isn't being commanded to operate.

Set the control knob to max heat. Remove the vacuum hose at the control valve and feel for vacuum with your thumb over the end of the hose. You should not feel any. Now select max cooling on the controls and check again. You should feel vacuum at the hose.

If the heater valve is operating properly but you're still not getting warm air when you ask for it then there are various possibilities to investigate.

Do you have the Delanair Mark II system, or the Mark III system? The change was made circa 1987. The easiet way to tell is the Mark III system has a 'pull for manual control' capability on the temp selector knob. The Mark II does not.

Cheers
DD

 

Also known as the heater valve.

Cheers
DD