Heater Fan, Won't run at full speed

Just read the self help file on this with the intention of replacing the transistors but !!!. The document says that the fan will still run at full speed due to the by-pass relay. Is this still the case for later cars. My symptoms are that it runs fine in manual for lower speeds but as you increase the speed it cuts out after a short while, say half a minute if lucky. Sometimes it won't run for a short while at all. I expected it would be the transistors overheating but not if there is a by-pass relay for top speed. Mines the later push button controls with ac. I was intending temporarily putting a volt meter on the signal feed with fan still attached to see what the control unit on the dash is doing as it may be that. Anyone come across this and have an answer to save me the time?

Hi Assich

The fan motor includes the control block with the transistors. From memory it has only 4 or 5 connection wires 2 of which are the power supply. I usually test out the functioning of a fan at this point using a direct power feed/jump lead with the fan speed rheostat recovered from an XM with manual heater controls. Do not have the fan loose in the footwell for this test as it can propel itself very forcibly about the car. Guess how I know. If all works with this test then before you set about the electronic control panel check out the state of the feed from F2 in the engine compartment. This feed can go high resistance and drop a lot of voltage when high current is drawn. It will even cause a manual control panel to malfunction but invariably upsets the functioning of an electronic control panel. In my experience it seldom does any permanent damage to the electronic panel.

As far as fuse F2 is concerned I have given up repairing/replacing the fuse/fusebox and now simply add another large 40amp fuse to the cooling fan stack clipped on the front of the battery box. There is a Citroen mod note that recommends retrospective uprating of this fuse to 40amp but I still do not think the small fuse/carrier is man enough to take this load long term hence my recent use of a physically bigger component.

John

This post has been edited by xmexclusive on September 22, 2008 06:02 pm

Thanks. When you refer to fuse F2 and about up rating it do you mean the 30amp fuse. My car is "young" enough to have had this fuse up rated since new. Interesting what you say about the feed to the motor though. Possible could test that by somehow liking straight to the battery with a suitable sized cable (jump lead) and connector to existing live wire at motor.

Hi Assich

I had trouble with my fan and here is how I resolved it. Might be worth a look. My fan worked for a while at only slow speed before it packed up all together.

Andy

Thanks will have a look at that too. Particularly since heater doesn't want to run at full speed. I checked Citroen's Laser system last night and the same control block on the fan was used in XM I and II's with aircon so I assume my relay isn't working. Played around with the controls in manual to see what happened this morning.

There are seven lights, one for each speed setting. One is the lowest and seven the highest speed. Fan runs fine on one through to five. Fan increases in speed when you go to setting six but after a while slows down gradually until it sits at around setting three. Go to setting seven at full speed and it just dies altogether and you have to go all the way down to setting three before it will start spinning again.

I doubt I am losing the feed signal over time as the lower settings work fine. It is possible just seems unlikely.

Hi Assich

I can confirm that the aircon electronics controller board is common to both Mk1's and Mk2's as some while ago I swapped the case on a Mk1 one to fit it up to replace a defective Mk2 controller. Looked in the junk box for the remains of my test rig. The rheostat on manual controller boards does not drive the board directly but is a low current device operating a couple of power transistors which then drive the heavy current transistors on the module in the fan. My next steps would be to try a known good fan then your controller board in a working car. Not options open to you I suspect.

John

I think F2 was upgraded from 30 to 40 starting from ORGA 7483, 1997/5/5. So if you have a 30A installed, someone replaced it after the 40A blew, perhaps. The 40A may be hard to get

Today I connected a volt meter to the control wire for the heater. Readings started at battery voltage when fan off and slowly reduced as fan speed increased - all using the manual controls. When I got to speed six it didn't drop much and when put to seven (full speed) it returned to battery voltage at 13.56volts. Turns out that the control panel on the dash changes resistance to earth of the control wire from the fan motor control unit. Thus I earthed the motor wire and the fan ran happily at full speed. Without doubt I need a replacement dash control panel or a by-pass switch for full blast.

I have connected a known good control panel with no change to what is happening. I assume something is giving the control panel a signal that means it switches the fan off. I also noticed it switched the a/c off at the same time.

Sounds odd. When you changed the panel, did that include the controls? If not, I wonder if the speed control is open circuit at the top end?

Peter.N.

Sorry! Iv'e just realised its an electronic one.

Yesterday was the first day this year that the outside temp didn't really get up much above freezing. I wonder if that may be something to do with what happened when I got in the car to go home from work. I have been putting the heating system to windscreen and switching to manual blower control up at light five to clear any mist on the screen initially. Yesterday the fan blew a little faster than before. Intrigued I then put it up to six and it blew faster again and then to seven and it really chucked out the air. Again this morning it continues to function as it should. Any ideas why it should suddenly start working properly?

I have spent most of my free day yesterday to solve the problem of non-working heater blower. Once extracted from its place, I took a good examination. It is a Bosch-made motor with brushes and two sleeve bearings. I found it rather clogged with fine dust and not turning smoothly. I guess this is the condition of most blower motors in PSA cars after ten years or so. This is also the reason why the motor draws more current than supported by its fuse, being it for heavy turning or for loose bearings, overheating and burning output transistors and the related fuse.
So I believe the approach to solving the blower problem should not be just electrical but should also include servicing the motor, otherwise high current draw will most likely cause melting fusebox and blown transistors again. What I did was to disassemble the motor, clean thoroughly, polish sleeve bearings, lubricate and put everything together.
When you're there, you can also put a car freshener tree directly at the air inlet for perfumed interior throughout the car!