I have a left-hand-drive 2004 Jaguar XJ Vanden Plas. With "dual" mode turned off and both sides of the car set at exactly the same temperature (68 degrees or so), the passenger's side seems to work fine, while the driver's side gets both less air volume and warmer air.

I've seen posts here about heat problems that seem to point to the heater core, but I'm not sure that's my issue. Could it be the blend door or something like that? And if so, can someone point me toward a resource to self-diagnose or fix it?

 

The usual cause is the heater core being partially blocked; I had to replace this on my last X350, but funnily enough not on the previous one. Replacement is not as huge a job as you might think. First the glove box is removed, then the heater fan module, exposing the heater matrix. When I had mine done in 2018 at the main agents they listed a kit as well as the matrix. What this kit contained I don't know, but it cost nearly as much as the matrix. Whether you get an independent shop to do it or not, it is important to make sure that any sealing rings are replaced at the same time. I can't remember the labour time, but it was something like 3-4 hours. Don't forget the coolant has to be partially drained as there are no valves to shut off the hoses, the heater matrix is hot the whole time even in summer.

 

The most common problems with the climate are:

Aux pump not working or not working 100% due to worn brushes or other electrical fault.

Blocked or partially blocked core.usually cold on driver's side but warm on pass. side

very rare-blend door failure due to wiring damage to motor.

also very rare- a piece of foam fallen off inside the 'box' and blocking flow.

I would tackle them in that order

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