P38A Is there a long term fix for the delicate HVAC blender motors?

My HVAC has been down for a while. Both blender motors (right and left) not happy.
Last weekend, finally got round to removing the easier to get to, but still quite hard left blender motor.
One of the solder points on the potentiometer had failed, so sorted that, and that side seems to be working now.

Going to tackle the right one this weekend, and hope it's something similar.

The problem is, this is just a temporary fix.
Looking through my history they've been changed twice before, so even when new only last about 7 years.

Is there a compatible blender motor off another car that just works?
Or maybe some override which stops the HVAC from caring so much about the potentiometer feedback.

I'd like to fix them properly once and that's it.
Is this possible?

The hevac needs to read the current draw and the pot feedback in order to work
The pots can be replaced with mixed success, but if the motor is worn out and pulling too much current (thinks it's jammed) then the hevac will set a fault

Montyjohn said:

My HVAC has been down for a while. Both blender motors (right and left) not happy.
Last weekend, finally got round to removing the easier to get to, but still quite hard left blender motor.
One of the solder points on the potentiometer had failed, so sorted that, and that side seems to be working now.

Going to tackle the right one this weekend, and hope it's something similar.

The problem is, this is just a temporary fix.
Looking through my history they've been changed twice before, so even when new only last about 7 years.

Is there a compatible blender motor off another car that just works?
Or maybe some override which stops the HVAC from caring so much about the potentiometer feedback.

I'd like to fix them properly once and that's it.
Is this possible?

Click to expand...

Failure is often caused by the blend flaps binding, the rubber edge wipers degrade.
If you turn off the "Auto" function, they have much less work to do and will last a lot longer.

Has anybody ever downgraded to the base model rotary knob HVAC unit?


I can't tell from the pictures if it uses cables or not to operate the flaps. If it does, I may be quite tempted.
I would also need to add the heated seat, windscreen and AC buttons which may or may not be a trivial task.

I was a bit more brutal and just hooked a wire through.. it worked.. mostly but very ugly.. but it was only for a while

Montyjohn said:

Has anybody ever downgraded to the base model rotary knob HVAC unit?

RANGE ROVER P38 1994-2002 HEATER MANUAL ROTARY CONTROL PANEL Hevac AWR 1009 | eBay

Part Number - AWR 1009.

www.ebay.co.uk

I can't tell from the pictures if it uses cables or not to operate the flaps. If it does, I may be quite tempted.
I would also need to add the heated seat, windscreen and AC buttons which may or may not be a trivial task.

Click to expand...

I have one in stock, it uses the blend motors.

Datatek said:

I have one in stock, it uses the blend motors.

Click to expand...

That's a real shame.
That really is over complicating the system for no reason.
I hoped it might be cable as when I removed the left blend motor the air box flap had a redundent arm on it that looked like a cable could be attached.

Something must work and fit because there's facility to attach a cable. But maybe on the RRC

Over-complicated Monty? I'll give you an even better example :

Up to the 1987 model year (ie from Oct '86) the cabin fresh air intake flap on the Classic was operated by a simple cable/slide lever system.
From that date this perfectly efficient & relatively bullet-proof mechanism was replaced by a vacuum operated electric solenoid controlled by a switch. The solenoid was un-obtainable for several years & when it did eventually re-appear as a 'special order' it was priced at just under 100 quid

Guess who bypassed the stupid thing so the flap remains open?
The trade-off is loss of the re-circulated air facility, but how often does anyone use that anyway?

I have found it's not the rubber edges of the flaps, but binding on the pivots in the sides & centre section of the heater box. Individually the L & R blend flaps are ok, but when the box is clipped together the shaft binds in the holes. The distribution flaps are a bigger issue. Again I have seen several that move freely when testing each pivot point, but the box being clipped together squashes the sides agains the shafts. I have checked with the gears removed & fitted. Found some solutions, and work-arounds but never a proper fix.

Have got a complete assembly on the bench at the moment, so will do some pictures this w/e to show the typical issue and how I sorted the flaps out.

The one I recently installed in Green P38 now moves the flaps easily with a tired 9V PP3 battery. HEVAC works as well with no errors.

Here's how I sorted the sticking flaps on two of my heater boxes. (One more heater box to sort in Blue P38)

Step-1 is to take the heater assembly out of the car (yes dash top has to come out), and disassemble it.
Step-2 is to enlarge all the pivot holes by about 0.5mm. For this you need 14mm & 10mm drills. Gently run the drill through the pivot holes in the centre & side casings. Then clean all the old grease & plastic shavings from the box.

These two pictures show the blend flaps. After the pivot holes have been freed up, it's worth filing or grinding away a few tenths mm from the casing where the flap goes in. This stops the flaps sticking when the casing is clipped back together.


For the distribution flaps there are six in total. (two screen, two face vents & two for floor vents) They all move together via the gears on the right side - hence why any one sticking messes the whole lot up.

These next two pictures show the face vent flaps. Again same process of easing the pivot holes a bit, plus take a fraction off the outer casing, so the pivot faces do not stick.



These two are the floor vent flaps. In the pic on the left below you can see the gap where I have relieved the moulding on the casing.


Now check each flap for easy movement.

It's also possible to wriggle them to check there's free play in the pivots:



Finally how to prevent the casing from binding when fully clipped together.

Note: there's various threads out on the interweb saying to do this with the heater in the car. NOT possible becasue it needs the front face off the heater box.

1. Assemble the box, making sure all the flap shafts go in the correct positions.
2. Put a couple of clips top & bottom to hold it together.
3. Put a small self tapping screw into the join just below the floor flaps. You can see the gap in the picture below which is roughly 1-1.5mm. This hopefully prevents the casing binding on the flap shafts.
4. When trying to fit the front cover, you will find it's difficult to locate the top. Start at the bottom, and install the screws in the order shown below.
5. Now re-check all the flaps move easily using your smallest finger !!