Heater Blower 4 Pin Connector Voltages (s2 Vsx)

Before I proceed with dismantling the heater blower I'd like to ask if anyone knows the correct voltages on the 4 ping connector to the heater blower. I am seeing 1.3 V on the red thick wire, not much on any of the others (70mV on one).

Engine fuse box was replaced back in 2007, new fuse in place but old one was OK. Just tried twisting the fuse contacts a little but no change.

I'd like to know of the 1.3 V is normal or if I have a problem (presumably not F2 in engine fusebox) with the supply to the fan.

regards

OK I checked there is battery voltage (13.8V) on the fuse F2 , but not on the fan connector. What else is there to check. Relay? Where are they? Anything else?

Thanks

Hi Tim,

Sorry, I wasn't ignoring your post. I must have missed it.

There is a degree of dependency on the model and year you're talking about and you didn't say which one of the XM's in your signature you're having trouble with.

The thicker two cables are easiest so we'll deal with them first:

The red cable is the mains live which starts at the battery and leaves the battery terminal on one of the two 6mm2 cables (not the big thick one which is the starter). It then travels to the fuse box in front of the battery tray. In there you will find Fuse F2. From Fuse F2 it then travels to relay 821 which is located under the glove box. From relay 821 the red wire arrives at the 4-pin connector plug on the blower fan motor. The coil for relay 821 is energised via the ignition key and Fuse F3 in the main fuse box in the passenger footwell. The return leg of that coil passes through a contact on relay 848 before returning to earth. Relay 848 in turn is only energised when the engine is running. It picks up a signal from the alternator to tell it when the engine is running.

So, in order for 12v to appear on the red cable at the motor, there must be power from the battery, Fuse F2 must be intact and conducting (including the connectors underneath the fuse box which normally corrode), Relay 821 must be energised which in turn requires Relay 848 to be energised, which in turn requires the engine to be running.

The thick black cable is connected to earth via two connectors in the harness. This should be grounded at all times.

The thinner two wires are orange and pink. These are signal wires.

On older cars they go straight to the rheostat on the back of the speed control knob on the dash. Therefore the voltage on both wires will vary depending on the position of the knob.

On newer cars with the automatic type of climate control both the orange and pink wires connect to the controller which is located behind the heating/aircon control fascia.

If you describe your problem in a bit more detail we might be able to diagnose where exactly the problem lies.

However, having said that, 99% of all problems with the heater blower are related to the supply coming from Fuse F2. Even if the fuse looks OK the terminals underneath the carrier are usually corroded. You have to remove the multi-coloured plugs form the bottom of the fuse box to see the damage. The other 1% of the time the heater matrix has leaked and the escaped water ends up flooding the speed control module in the fan motor housing when it sloshes over to the left when going around a right hand bend.

Hope that gives you some food for thought.

Cheers

noz

As Noz says, look at the back of the fuse box, I have recently spent a week chasing an ABS fault which I eventually found to be due to the wire corroding away. Even though the fuse box has been replaced the connectors can corrode.

Peter

Thanks for the input guys Noz it is the R Reg S" VSX that has this particular problem I'm off to check the back of the fusebox and then try and locate relay 821, thanks again/.

Sorry, Dr Tim, I didn't see the S2 VSX in the title of your post.
Cheers
noz

OK so I went in behind the engine fusebox, rather too tight in there to get a voltmeter in but I did managed to replug the appropriate plug. Back inside, initially thought again no 14V, but eventually after some very weird readings started seeing 13.8V between the thick black and red wires. Now Its possibly always been there and just my voltmeter incompetance, but I have measured this many times before in recent months...

Anyway, tested the motor with the big multiplug in but not the little one wire one. Did not spin (had it on the floor resting between 2 soup cans). Does it need the little one wire plug connected to spin?

If not as I suspect then its back to disassembling the damn motor I guess. Currently attempts have been foiled as I can't get the black single connector that plugs into controller board out!

This post has been edited by DrTim on July 04, 2010 09:19 pm

OK scrapped the Prestige earlier today :-(

Grabbed the heater blower and put that in the R Reg Vsx just now. Still no no blowing!

OK so there is battery voltage on one wire. To much rain to do any more today.
Need blower as demisting is definitely an issue in weather like this.

Any advice welcome

DrTrim, yes the single wire connector should be connected also. This is feedback for motor speed to the A/C ECU.

Also check that between thick wires you have 12V when the motor is supposed to turn - if you have bad connection somewhere, under load the voltage can drop to ~0V.

This post has been edited by Sharo on January 14, 2011 02:55 pm