2004 XJ8 not blowing out hot air into the car

SOURCE: 1998 xj8 heater only works when engine at higher revs

There is an Electic Water Pump for the Heater that is located under the hood near the left fenderwell. If it's not a fuse, then likely, this pump is bad. Mine went bad in my 1999 Jaguar XJR. It runs close to $400 for the pump, so hopefully that's not the problem. Price does not include labor.

Since I'm comfortable with Electronics, I replaced the brushes in my motor and it works fine now. Heat all the time and only cost $1.00 You may be able to find a shop to rebuild the motor for you at a fraction of the cost.

SOURCE: 2004 RX-8 Air Conditioning Blowing Hot

The A/C control is fixing to go out. the whole modual replaced and the problem will be fixed...

SOURCE: 2004 chevrolet suburban AC blows hot/cold at same time

You need to replace the drivers side temp actuator that is located on the left side of the HVAC box. It is retained by 3 screws and is fairly easy to replace.

SOURCE: AC BLOWER NOT BLOWING

The resistor that controls the blower motor. it is a small gadget that has a 2 or 3 wire plug . Replacing the resistor should fix your problem. It is on or near the blower motor. Under the dash. Not easy to remove . But it can be. Please give thumbs up if helped.

SOURCE: I have a 2004 Pontiac

Sounds like your cooling fans on the radiator are not working. The fans are activated by a thermol switch on the engine or radiator reading the coolant temperature and an A/C switch. When the coolant is too hot the fans should activate cooling the system down. And, when the A/C is on the fans should also activate in order to cool the condensate so the A/C would work.

When you are driving, the movement of the vehicle throught he air is providing enough air flow to keep things cool and functional.

I would check the radiator fan fuse or fuses first. If those are OK I would try to run the fans with 12 volts and a ground that I supply just to see if the fan motor(s) actually run when powered. If the fan don't run when powered then the fans are bad and will need to be replaced. If the fans do run when you power them manually, then something is not allowing the power to activate, like a relay, control unit, or wiring.

It will take a little diagnostics, but it is not too difficult to chase it down.