Blend Motor / Hevac P38 woes

**MoodyBlue** · 6th December 2008, 08:55 PM

Anyone done any work / investigative fault finding etc on their P38 Blend Motors and/or Hevac unit.

The fault book symbol was lit up when I bought my P38 a year ago.

I purchased a new set of blend motors on ebay and fitted them.

All was fine for 6 months, then it started playing up again. Computer says "Left Blend motor" so I changed it and all was well again for a month or so.

Then the left blend motor again went screwy.

Sick of the expense, I used one of the original blend motors, and for a while all was well.

Two weeks ago back to the old cook the passenger and freeze the driver routine.

I purchased a new left blend motor and fitted that. The joy lasted about two minutes.

Now I have purchased another Hevac control which is on its expensive trip from the UK.

Meantime I dissected the blend motors I have on the bench.

Sorted through the wires and find that applying 12 volts to the motors they happily move through the full travel that they are supposed to.

Next the Variable resistors (Pots). These are 10k stamped. When applying a multi-meter to each one and cycling them from zero to 10k they all seem to read correctly approx. Four of them read from zero to approx 9.5 k and one reads zero to 10k exactly. Anyone have advice as to whether the 9.5k reading is the cause of the problem??

Now have the blend motor plug off the back of the hevac unit and by using two wires from a 12 volt battery can cycle the blend motors to get the air balance and temp in the cabin correct, but its no longer automatic.

Thanks
Jeff

**p38arover** · 6th December 2008, 10:20 PM

I doubt the 9.5Kohm reading is the problem. Pots aren't that accurate anyway.

I pulled apart the motor on my faulty servo and found the brushes were almost worn away. I replaced it with a second hand servo and 6 years on it's still working.

Does Romsey LR Service Centre have any second hand HEVAC panels you could try?

**MoodyBlue** · 7th December 2008, 07:29 PM

Ron,
I thought by fitting a set of three new ones I would have solved the problem for a long time (life of the car according to Ray at Romsey LR)

Any way all four spare ones seem to move through the cycle with-out any apparent hesitation.

I've already got another Hevac on the way from the UK.

Cheers for now

Jeff

**Scouse** · 8th December 2008, 09:46 AM

Has the fault actually been diagnosed as blend motors ?

Is the HEVAC coming from the UK the latest spec ?
JFC102540 ?

**adm333** · 9th December 2008, 11:39 AM

The display LCD on my hevac controller became dodgy, not displaying all of the numbers correctly so I just bought a 2nd hand hevac controller from a wrecker for about $200.

The cheque book symbol kept popping up as well and turned out the other issue I had was that I needed to replace the recirculation flap motors.

Could these be part of your problem ?

**MoodyBlue** · 9th December 2008, 06:37 PM

Hevac from the UK is just same year from wreck.

Fault check by Ray says open circuit on left blend motor.

This was AFTER fitting a brand new one

.

So also got another plug and wires that are normally on the end of the three motors.

Hevac is not here yet, but thinking of trying new plug as well, just in case one of the pins is not making contact.

**Scouse** · 10th December 2008, 10:04 AM

There's been quite a few HEVAC supercessions over the years. JFC102540 is the latest one that I know of (for the earlyish cars anyway).

**Hoges** · 27th December 2008, 02:26 PM

Sorry for the late response...have you trawled through the HEVAC material in the RR.net forums? lots of coloured photographs etc etc It may not be the blend motors as much as a sticking flap caused by heat distortion of the plenum chamber due to our sunny climate. The constant stress on the blend motors forcing against a binding flap may cause their early demise...

There's a simple and effective fix on RR.net wherein a heavy gauge self tapping screw is inserted to spread the chamber a fraction and stop the flap binding...it works!

**HSE30** · 29th July 2009, 01:02 PM

Originally Posted by MoodyBlue

Anyone done any work / investigative fault finding etc on their P38 Blend Motors and/or Hevac unit.

The fault book symbol was lit up when I bought my P38 a year ago.

I purchased a new set of blend motors on ebay and fitted them.

All was fine for 6 months, then it started playing up again. Computer says "Left Blend motor" so I changed it and all was well again for a month or so.

Then the left blend motor again went screwy.

Sick of the expense, I used one of the original blend motors, and for a while all was well.

Two weeks ago back to the old cook the passenger and freeze the driver routine.

I purchased a new left blend motor and fitted that. The joy lasted about two minutes.

Now I have purchased another Hevac control which is on its expensive trip from the UK.

Meantime I dissected the blend motors I have on the bench.

Sorted through the wires and find that applying 12 volts to the motors they happily move through the full travel that they are supposed to.

Next the Variable resistors (Pots). These are 10k stamped. When applying a multi-meter to each one and cycling them from zero to 10k they all seem to read correctly approx. Four of them read from zero to approx 9.5 k and one reads zero to 10k exactly. Anyone have advice as to whether the 9.5k reading is the cause of the problem??

Now have the blend motor plug off the back of the hevac unit and by using two wires from a 12 volt battery can cycle the blend motors to get the air balance and temp in the cabin correct, but its no longer automatic.

Thanks
Jeff

Hey Jeff, just saw your post. Check that the doors themselves are not binding in the duct. I had one is the workshop that kept destroying servo's. It turned out to be two doors getting caught in the duct. I sanded the doors down to give some clearance, which fixed the problem.
Regards Russell.

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