[Jakeiscrazy]

I have a weird issue. My blower motors have stopped blowing. On startup they blow for a few seconds and then abruptly cut off and I get the good old Testbook Symbol on the HVAC controller. Sadly I don’t have Nanacom or similar.
Adding to the weirdness is that one out of every 50 or so starts the blower motors keep blowing and act as if there is no issue at all! When I turn the car off and on they go back to not working.

Some things I've already tested:
Relays- swapped them out for new ones with no change.
Fuse box - brand new just replaced
Alternator - Just replaced and making a prefect 14 volts.
Battery - Also fairly new and likely not the cause.

Other factors - I have my left blower motor disconnected. It's burned up my original fuse box (as is so common #britishwiring) and even after replacing the fuse box and motor, it was still pulling far too many amps. I suspect damage to the power wire is causing far greater resistance than is normal. I will be replacing it soon. However I have run the system with only one motor in the past. So, I don’t think this is an issue.

Thanks in advance!

 

[Jakeiscrazy]

Have I stumped everyone? I know not having Nanacom makes this one hard but I'd take even a complete guess just to have something to chase.

 

[Richard_G]

At a guess I'd say that the feedback circuit is faulty. The HEVAC will spin up the blowers on first start up, the same as it moves the blend motors, and check that it gets the correct feedback. If it doesn't, it logs it as a fault, brings on the book symbol and doesn't try to use the blowers again. Having one blower disconnected is about the same as having neither working. One blower sucks in air, blows it towards the heater matrix but as there is no air coming from the other side to join it, the airflow simply bypasses the matrix and blows straight out the other side. With only one blower working the only way you get any airflow is by putting it into recirculate so the vents at each side are blocked off.

 

[Jakeiscrazy]

At a guess I'd say that the feedback circuit is faulty. The HEVAC will spin up the blowers on first start up, the same as it moves the blend motors, and check that it gets the correct feedback. If it doesn't, it logs it as a fault, brings on the book symbol and doesn't try to use the blowers again. Having one blower disconnected is about the same as having neither working. One blower sucks in air, blows it towards the heater matrix but as there is no air coming from the other side to join it, the airflow simply bypasses the matrix and blows straight out the other side. With only one blower working the only way you get any airflow is by putting it into recirculate so the vents at each side are blocked off.

Thanks I'm going to give that a shot!

 

[Richard_G]

Give what a shot? If you've got one blower disconnected the HEVAC is seeing no feedback from that so that would bring on the book anyway. Replace the one that doesn't work and reconnect the one that is disconnected. How can extra resistance cause it to draw more current? Ohms Law, I=V/R (Amps=Volts Divided by Resistance) so an increased resistance would reduce the amount of current being drawn not increase it.

 

[marty_nz]

Check the power feeds to the blower motors in the RHF footwell behind the kick panel. They can corrode out, and that will cause issues including burning out the fusebox.

Mine were corroded, including into part of the cables - so I cut the connectors out and crimped the wires back together.