DB7 3.2 Heater problem

[peter webb]

Hi
Can anybody help

Heater of DB7 only blowing cold air.

Appears that when I turn from hot to cold with the switch it just stays on cold. The switch is not loose

Any ideas would be greatly appreciated

Thanks

Pete

[drmw]

I don't know anything about that model, so the following based on previous episodes with other cars:

Check coolant level
If climate controlled, check cabin temp sensor(fluff etc)
My previous mercedes had an auxiliary water pump that once stuck - with engine running & warm, ramping control from one extreme to the other several times encouraged it to start working again

good luck - not the time of year for this fault!

[V8LM]

The vent valve can get stuck. Give to top of the dash a good wallop.

[smudger186]

hi there, could you give me a bit more info, when you turn from cold to hot is there no hot air at all? when you turn the direction switch do the heater ducts turn off as expected?
If you get somebody in the car with the engine warm, to turn from cold to hot watch under the bonnet at the rear of the inlet manifold to see if the heater valve [located there]moves accordingly.
Could be a faulty heater tap,loss of vacume to system,stuck heater flaps,blocked heater matrix,plus other faults!!!
hope this helps

[StephenP]

V8LM said:

The vent valve can get stuck. Give to top of the dash a good wallop.

Try this first .... common DB7 issue apparently so give the air con unit a tap on the side...

[Grom1t]

There is a vacumn controlled valve that sits close to the rear of the inlet manifold that can get jammed, this is a common jaguar item fitted to XJ jags up to xj40 and XJS's, here,s a new one on eBay.

http://www.ebay.co.uk/itm/JAGUAR-XJ40-HEATER-VALVE...

Locate it, look under the inlet manifold close to the bulkhead or just chase back the 1/2" water pipes back from the bulkhead, start car to create a vacumn and switch to full hot and make a note of the operating arm position on this valve then full closed and check the arm has moved.

It works with a diaphragm which will perish with age, after 16 years it will be fragile by now.

Hitting the heater box just changes where the air is directed.

If the pipes are hot both sides of this valve then matrix may be clogged, a good back flush and use a decent descaler should clear most of the rubbish out and save a dash out repair.

You can prove the control inside the car by pulling off the thin black vacumn pipe, in either fully hot or fully cold I forget which you should feel a vacumn pulling on this tube.

Regards

Edited by Grom1t on Monday 12th November 23:47