Xantia Air Con - blower permanently on

[Old-Guy]

The VSX's (1998) air-con blows cold OK, but even on hottest setting, is stuck permanently on full chat (not a problem on a sunny day) and can't be turned off. None of the controls have the slightest discernable effect eccept the screen/face/feet direction. Is this the well-known sensor-fan problem?

[Xaccers]

When you say the air con is on, do you mean the air con (ie compressor is permanently engaged) or do you mean the blower is on full blast?
If it's the latter then the transistors need replacing on the blower's control board, it's a known issue with Xantia blowers.

[Old-Guy]

Thanks Xac - never had a car with A/C before (in the days when I had new(ish) cars, I regarded it as just something else to go wrong that I couldn't fix myself), and the attitude has stuck.

Anyway, the blower is on full blast all the time - I'll have a search of the forum for "blower transistors). I'm pretty good with a soldering iron but it's not top of the list now.

[Xaccers]

If it's blowing cold air when the a/c button is pressed (in the engine compartment at the top of the black cylinder with the brown plug on the side there should be an inspection window, unless the dryer has been replaced by an aftermarket one, you should see something flowing through the glass) then make a mental note to have it re-gassed in the winter when the prices are 1/2 what they are in the summer, as chances are it'll be in need of new oil and probably some gas.

From recent posts there are replacement transistor boards on ebay but they're using the wrong transistors.

[isisalar]

A dodgy fan speed controller was one of the first things I had fixed when I got my HDI back in December. There was one in stock at a local(to the repairer) factors and was fitted to the fan motor quite quickly. It certainly wasn't a major job.IIRC the part was about £70 but I have since found that this place tends to double the price of any parts they supply. I shortly after saw the same part on e bay for about £17. Anyway they're available and not that expensive or difficult to fix.
Best of luck with the new car.
Cheers
Paul

[Old-Guy]

Thanks for your patience with my stupidity - dog tired yesterday: French farce + trip to London to buy the car + streaming allergy to rape-seed pollen (I think).

To wrap it up, the air-con works fine though the switch doesn't light which confused me (easy). Talking to the previous owner, already diagnosed as the blower speed control board. I'll start a new thread.

[Xaccers]

The bulb could either have blown or the coloured cap could have burnt too much to let light through.

[Old-Guy]

Thanks for your patience with my stupidity - dog tired yesterday: French farce + trip to London to buy the car + streaming allergy to rape-seed pollen (I think).

To wrap it up, the air-con works fine though the switch doesn't light which confused me (easy). Talking to the previous owner, already diagnosed as the blower speed control board. I'll start a new thread.

No I won't. For the benefit of anyone who finds this thread: some years ago, Jim wrote a concise guide to Xantia Blower Speed Controller Module Repairs and subsequently Xantia Blower Fan Speed Control: Testing.

I'll start with the last one to make sure the diagnosis is correct!

[Old-Guy]

Started to make a list of 'bits' for a service of my new 2.1 VSX. Wondered if the pollen filter needing changing, so nipped out to check. The slider was well stuck in place - suggesting it hadn't been moved for a long time! (Note 1998 2.1 VSX - no screws). It took both hands to move to it, and when it did slide off, a pile of dead bugs and bits of leaves fell onto the nice clean footwell carpet. Not promising. When I got it out, the filter is absolutely choked; I'll add a picture of it to the list to be uploaded later. Filter is dated May 02 so it has been changed at least once, but probably not in the last 10 years

Might this having something to do with the blower fan (presumably) cooking the speed controller?

The air-filter screws are well rusty and soaking in penetrating oil before I attempt to undo them, so I added an air filter to the list too.

[Old-Guy]

Interestingly, I've got a bill dated 7/10/2008 for a new heater blower. So a new blower was fitted without checking/changing the pollen filter. Could the blower speed control transistors expire because the motor is drawing extra current as it struggles to such air through a blocked filter.

I shall be very interest to see if the new filter dramatically improves the rather feeble air flow (on through-flow rather than re-circulate) to a mighty blast (the fan makes enough noise!).

[Mandrake]

If the filter is before the fan motor I doubt a blocked pollen filter would cause the motor to draw more current - with a partial vacuum there will be less load on the fan due to lower air pressure and it will speed up! Think of a vacuum cleaner with the suction pipe blocked - the motor speeds up considerably, which is a sign its under less load and will be drawing less current.

By all accounts the blower speed controller transistors blow simply because the controller is a marginal, poorly executed design. I seem to remember Jim saying that it has a pair of paralleled power transistors that don't even have load balancing emitter resistors, so any small imbalance between the two transistors will cause one to carry most of the load and fail first causing the second to rapidly fail afterwards...

Water getting into the controller is also an issue with leaking window scuttles.

[Old-Guy]

Water getting into the controller is also an issue with leaking window scuttles.

The screen was replaced in 2010, so I hope it was bonded properly.

Last night I sat down and listed the last 8 years MoTs and bills. Since 1/1/2008 (4 years), it's also had new discs and pads all round, HP pump, A/C pump & re-gas, alternator, radiator, battery, O/S suspension arm assy., drop links, both track rods and ends, crankshaft pulley, glow-plugs, belts and tensioners, various pipes and hoses, etc. etc. Though I'm not that impressed by the quality of the servicing as the pollen filter hadn't been changed for about 10 years!

Just ordered the bits for the blower speed control rebuild, and I'll do the blower relay mod. at the same time.