Hot and cold feet but only cold face

XJ40
1

I checked my heat out yesterday …down in the footwell I could hear the servos operating and I got heat and A/C down there when I changed the setting …however, my centre vent stays open all the time and the side vents/windshield vents only do A/C.
So I think this must mean that the centre vent door has broken?

2

Larry …

The center vent, two side vents, and two demister vents all receive the same temperature air from the
evaporator/heater box. The only time the center vent is commanded open is when cold air is selected.

The vacuum actuator that operators the center vent is designed to hold it closed by a big internal spring and uses vacuum to open it. When the actuator fails (they usually just split open) the spring now permanently keeps the vent closed.

The entire dash top has to be removed to replace the center vacuum actuator. With the top off you can also access the two demister vents which may also be broken. A cheap fix is to remove the center grill and wedge something in the vent door to keep it open, usually a short piece of heater hose.

3

The centre vent is open all the time, Groove. When I had heat up top, heat came out of the centre vent too. It worked properly for many years but this year I can’t get any heat to face vents screen or centre, just to feet.

4

Sounds like the upper blend flap (actually a partial cylinder) is not working. Could be a defrost flap has broken and fallen, jamming the blend cylinder from rotating, or the upper blend actuator (right side of the climate control unit [CCU]) could be playing up, or the upper blend potentiometer (left side of CCU) could be faulty. Heard of all three happening, and there are numerous posts in the archives about these issues. Do you have the CCU service manual?

1 Like
5

Larry …

Everything you could possibly want to know about the XJ40 HVAC system. Although there may be some very small differences over the model years it’s basically still the same.

Ignore all the flashing green buttons and only select the blue “Download” rectangle button. Wait a few seconds and it will open up.

1 Like
6

Thanks guys, I think I’ll pull the centre vent first and see if if can get my hand down inside - thanks for the download link btw