P38A Hevac.....🤬

Hevac bolloxed??
Blend motor open circuit to positive.
The motor works including a second motor wired up.
The potentiometer no feed back
Checked and works after resolder.

I've fitted second blend unit and I have the same motor short issue ..
I really don't want to pull the flipping centre console as it breaks every time I do...effing thing.
Both motors bench tested and function in both directions.
The flap is moving surprisingly freely as well ...
Damaged hevac internally?

Even with a blend motor disconnected it still showing a short???
Nothing has been moved or worked on for a while in this area to suggest an outside affect..
The fault will not clear at all.

Mark Piercy said:

Even with a blend motor disconnected it still showing a short???
Nothing has been moved or worked on for a while in this area to suggest an outside affect..
The fault will not clear at all.

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Is this your car or Elliots?

Mine this time Keith
Everything does as it should but this fault.

Also to add, when the ignition goes on the hevac comes online , it the clicks and throws the book up straight away and every time.

In my opinion, either the HEVAC fault detection is a bit "could be this or that" type software, or the messages in Nanocom are equally vague. I find using the utility to drive the motors & see the feedback is more useful than the fault messages. Best way is to unplug from HEVAC. Then connect an ohm meter, and drive the motors with 9V battery.

I've had short-circuit to ground (i.e. zero volts from pots), and other messages, when the real fault was dodgy socket contacts in the plug that connects the motors to the HEVAC They were not corroded, but loose on the pins when plugged in !! I have since replaced several contacts, and all three motors now work & give good feedback in Nanocom.

Also found one faulty potentiometer a while back. My quick fix was to steal a pot from a spare blend motor. I now have some replacement pots, so will be repairing the spares as well !!

16-pin connector.

Mark Piercy said:

Also to add, when the ignition goes on the heavy comes online , it the clicks and throws the book up straight away and every time.

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I would test as suggested by pwood999. The HEVAC is a pretty robust unit, I would suspect connectors or wiring if it's actually not a blend motor.

We know the HEVAC uses motor current to find the end points during calibration, but it's not clear if it also checks current to tell if the motor is open circuit or short. Open circuit on the feedback pot will either be 0V or 12V (could be 5V) depending on which side is open. Remember this is early 1990's software but we cannot be sure if it's written by Valeo or LR !!

Nano & Faultmate could even give different faults ?

I'm thinking that way also, the wiring at the plug behind the heavy.. even with the motor disconnected completely I getting same fault

Thank you both

pwood999 said:

We know the HEVAC uses motor current to find the end points during calibration, but it's not clear if it also checks current to tell if the motor is open circuit or short. Open circuit on the feedback pot will either be 0V or 12V (could be 5V) depending on which side is open. Remember this is early 1990's software but we cannot be sure if it's written by Valeo or LR !!

Nano & Faultmate could even give different faults ?

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There are or were some bugs in the Nano firmware that I have not seen on Faultmate.

Mark Piercy said:

I'm thinking that way also, the wiring at the plug behind the heavy.. even with the motor disconnected completely I getting same fault

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That rules out blend motors then. It only needs traces of corrosion in the connectors or on the PCB to cause problems.

Datatek said:

There are or were some bugs in the Nano firmware that I have not seen on Faultmate.

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A while back on mine I had a known potentiometer fault on r/h blend motor but when we tried to move it with Nanocom it moved the L/H. Replaced with good blend motor and Nano would move it. Seems when fault on one side Nano ignores that side and goes straight to the other

Rubberknees said:

A while back on mine I had a known potentiometer fault on r/h blend motor but when we tried to move it with Nanocom it moved the L/H. Replaced with good blend motor and Nano would move it. Seems when fault on one side Nano ignores that side and goes straight to the other

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I've seen that as well - hence why I started using 9V battery !!

When i was trying to diagnose blend motors with nanocom, forcing appeared not to work as i anticipated.
I came to this conclusion below, but only based on what i observed and not on knowledge of the software
If you start with both motors at 50% and command one to 100% or 0% then they will both move.
My reasoning is that the hevac software overrules what the nano asks and maintains the software rule that both sides must be within 2c of eachother. Ie, nano does not force movement but in fact overrides the temp control. For example if you set RHS to force100% the hevac behaves as though you selected HI and overrides the LHS to 2c lower, which is 27c

kermit_rr said:

When i was trying to diagnose blend motors with nanocom, forcing appeared not to work as i anticipated.
I came to this conclusion below, but only based on what i observed and not on knowledge of the software
If you start with both motors at 50% and command one to 100% or 0% then they will both move.
My reasoning is that the hevac software overrules what the nano asks and maintains the software rule that both sides must be within 2c of eachother. Ie, nano does not force movement but in fact overrides the temp control. For example if you set RHS to force100% the hevac behaves as though you selected HI and overrides the LHS to 2c lower, which is 27c

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Yes correct, but the max difference is 6degC not 2degC !!

Ok, plugged in a spare baron unit and at first and the same problem arose. So .... I messed with the plug..(as suggested) and pfff... It responded!!!! Tomorrow at some point between work, shopping and stuff I'll plug mine back in after giving the plug some attention and see if it remains a problem of connection!!!
Thank you very much all your suggestions and help.
I very much appreciate it

Mark Piercy said:

Ok, plugged in a spare baron unit and at first and the same problem arose. So .... I messed with the plug..(as suggested) and pfff... It responded!!!! Tomorrow at some point between work, shopping and stuff I'll plug mine back in after giving the plug some attention and see if it remains a problem of connection!!!
Thank you very much all your suggestions and help.
I very much appreciate it

Click to expand...

Was it a red baron?

kermit_rr said:

Was it a red baron?

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It was and he was a bugger to catch

Mark Piercy said:

It was and he was a bugger to catch

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Thought that was a pigeon?