P38A blend motor

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kermit_rr said:
Bit more investigation...
If i set the passenger blend motor (now working) to 100% and also the distribution motor to 100%, the value registered on nanocom is 100 and 105 respectively. If i manually turn the pot on the driver side motor, the value goes from 0-92
I'm wondering if this is the problem? The hevac doesn't see a high enough value and marks it bad?
Click to expand...

How are you doing this? When you do a calibration the the blend motor is driven in both directions until the flap hits the stops at either end and the motor stalls. This tells the HEVAC ECU what the full travel of the motor/flap is. Full travel in one direction will then be regarded as 0% and full travel in the other direction 100%. The full travel of the pot is never used. That is why the motor must never be powered (ignition turned on) unless it is in position. The stops on the flap prevent over rotation and damage to the gears and pot.
 
Last edited:
wammers said:
How are you doing this? When you do a calibration the the blend motor is driven in both directions until the flap hits the stops at either end and the motor stalls. This tells the HEVAC ECU what the full travel of the motor/flap is. Full travel in one direction will then be regarded as 0% and full travel in the other direction 100%. The full travel of the pot is never used. That is why the motor must never be powered unless it is in position. The stops on the flap prevent over rotation and damage to the gears and pot.
Click to expand...

Agreed - if you let the HEVAC power the blend motors when the motor is not installed it will go outside the calibration parameters. To recover that, use the 9V battery to get the white boss back to mid range (flat side parallel to edge of box, and then install the blend motor. Clear the faults and if you're lucky all will be well, and/or you may require a re-calibration. Don't give up, sounds like you're not far off
 
wammers said:
How are you doing this? When you do a calibration the the blend motor is driven in both directions until the flap hits the stops at either end and the motor stalls. This tells the HEVAC ECU what the full travel of the motor/flap is. Full travel in one direction will then be regarded as 0% and full travel in the other direction 100%. The full travel of the pot is never used. That is why the motor must never be powered (ignition turned on) unless it is in position. The stops on the flap prevent over rotation and damage to the gears and pot.
Click to expand...
I put the motor in place, turn the ignition on and let it do it's cycle. With the ignition still on and nanocom connected, i take the motor off, take the lid off and with the white gear removed i can turn the pot freely and see the value change on the nanocom from 0 to 92 or anywhere in between.
If at this point i select HI on the passenger blend motor, the value increases to 100 and if i select 'screen only' on the distribution, the value goes up to 105, or 0 for the face level vents.
When i turn the ignition on, blend motor in place, it cycles to cold, then to hot and stops. At this point the value in nanocom is only 72, so nowhere near the max of 92 from above. I've tried putting it back together in the max hot position with the pot in the 'wrong' location to get it closer to the max value ~89 or 90, this made no difference.
I've just check the new pot over soldered in place has the same degree of sweep as the old one i took out so it's not a case of more or less movement available
 
kermit_rr said:
I put the motor in place, turn the ignition on and let it do it's cycle. With the ignition still on and nanocom connected, i take the motor off, take the lid off and with the white gear removed i can turn the pot freely and see the value change on the nanocom from 0 to 92 or anywhere in between.
If at this point i select HI on the passenger blend motor, the value increases to 100 and if i select 'screen only' on the distribution, the value goes up to 105, or 0 for the face level vents.
When i turn the ignition on, blend motor in place, it cycles to cold, then to hot and stops. At this point the value in nanocom is only 72, so nowhere near the max of 92 from above. I've tried putting it back together in the max hot position with the pot in the 'wrong' location to get it closer to the max value ~89 or 90, this made no difference.
I've just check the new pot over soldered in place has the same degree of sweep as the old one i took out so it's not a case of more or less movement available
Click to expand...

The pot travel means nothing it never travels the full extent of the pot. It is how far it travels when in position that counts. Put it back together and do a calibration with Nanocom. That should tell the ECU the full extent of travel of the flaps in both directions. Then set a mid position on the heat controls when ignition is switched on motor should cycle then go to mid point or thereabouts.
 
wammers said:
The pot travel means nothing it never travels the full extent of the pot. It is how far it travels when in position that counts. Put it back together and do a calibration with Nanocom. That should tell the ECU the full extent of travel of the flaps in both directions. Then set a mid position on the heat controls when ignition is switched on motor should cycle then go to mid point or thereabouts.
Click to expand...
Once it's done a cold/hot cycle, it won't move when i select calibrate.
 
Think I've found it!
Ignition on, let it get to the end of one cycle, ignition off. Motor off and a quick check, i can feel the flap is all the way across.
Back on, ignition on for the next cycle, ignition off as soon as it stops. Take the motor off and the flap hadn't moved the full extent of its travel!!!
Progress!!
If I'm very gentle, i can feel the flap catch ever so slightly. When the motor is on, it must be enough to cause a jam!!
Let me guess, it's entire dash out if i want to fix this :rolleyes:
 
kermit_rr said:
Think I've found it!
Ignition on, let it get to the end of one cycle, ignition off. Motor off and a quick check, i can feel the flap is all the way across.
Back on, ignition on for the next cycle, ignition off as soon as it stops. Take the motor off and the flap hadn't moved the full extent of its travel!!!
Progress!!
If I'm very gentle, i can feel the flap catch ever so slightly. When the motor is on, it must be enough to cause a jam!!
Let me guess, it's entire dash out if i want to fix this :rolleyes:
Click to expand...

Is the hole warped slightly so the flap is catching.
 
kermit_rr said:
Think I've found it!
Ignition on, let it get to the end of one cycle, ignition off. Motor off and a quick check, i can feel the flap is all the way across.
Back on, ignition on for the next cycle, ignition off as soon as it stops. Take the motor off and the flap hadn't moved the full extent of its travel!!!
Progress!!
If I'm very gentle, i can feel the flap catch ever so slightly. When the motor is on, it must be enough to cause a jam!!
Let me guess, it's entire dash out if i want to fix this :rolleyes:
Click to expand...
eightinavee put a fix in the tech archive, I think it was for the distribution flap though.
 
Datatek said:
eightinavee put a fix in the tech archive, I think it was for the distribution flap though.
Click to expand...

Never known a temp flap to stick but i suppose there is always one. Distribution flaps stick but only the rear one. Someone suggested a screw to spread the casings apart as a stop gap method. But stripping the unit is the only proper way to do it. Grease goes hard and seizes the pivots.
 
wammers said:
Never known a temp flap to stick but i suppose there is always one. Distribution flaps stick but only the rear one. Someone suggested a screw to spread the casings apart as a stop gap method. But stripping the unit is the only proper way to do it. Grease goes hard and seizes the pivots.
Click to expand...
it feels like it catches on a join, its worse if i apply pressure to the lever in the direction of the centre of the car, I'm surprised its enough to cause a problem though as the blend motor offers more torque than i can stall with my fingers holding the output shaft. Otherwise the movement is free and loose
 
Holy thread resurrection, batman!!
Time to dig up this old thread, what with cooler times approaching.
The only fault i have worth hevac is distribution motor stall position. However the flap operates just fine.
Passenger temp/blend flap works just fine and adjusts up and down with the temp control buttons.
Drivers blend flap moves fully one way then fully the other and stops until the ignition is cycled again. Nanocom reports it is stopped at 77% and the calibration button doesn't activate the motor, neither does the 'force' option.
I've noticed if i force the passenger motor to a value, the distribution motor also seems to activate.
Does this mean the hevac unit is probably goosed? I know wammers suggested this earlier in the thread but wondered if there's anything else i can do or check before searching ebay for someone else's hevac unit that works even less than mine!
 
Thought I'd got to the bottom of this when i found a hairline crack in a solder joint in the blend motor!!
Alas, still goes to cold, then to hot and stops.
Still no fault recorded :(
 
SOLVED!!!

The blend motor send fine, pot tested out, couldn't find any problem.
Replaced with another, pot feedback was very similar but the book symbol stayed off.
I can only assume the feedback/current draw from the actual motor was outside spec
 
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