Another Recirculation Motor Issue

Hi all,
P38 1999 4.6 , i have changed all Hevac motors and the right Recirculation motor is driving me crazy.
It works , tested with 9v battery goes fully open and fully close with nice and smooth , once it's hooked at its harness it seems dead. So I got the old one with no gear (only the motor and the small circuit) and it works (at least it spins as soon as I put ign in pos 2).
Nanocom gives me rh recirculation motor shortcut .
now the questions!!
how much i current is fed at the rec. motor ?? (could be low current issue)
how the motor feels the open and closed position ??
is there any tip when replacing the motor ? (has to be replaced fully open or fully close??)

Thank you all!!!!

It should be assembled with the 2 alignment marks on the gears pointing at each other. Then the flap should be positioned so you don't need to force the motor.

Some of the HEVAC faults are / can be caused by intermittent contacts on the plug feeding the motors.

Great I'll check for the marks tomorrow.. thanks

No marks at all... I found that current flows +/- and not vice versa .. it opens but doesn't close the flap.. so I believe I must focus on the hevac module.
From RR literature the recirculation push button feeds current to the motor until it reaches the full open position , once depressed it feeds the current inverting +/- until it reaches the full closed position .
do I miss something??
As far as I know as soon as the ign pos reaches pos 2, Hevac should self test positioning recirculation flap to match the push button in open position is it right?

greasemonkeylab said:

No marks at all... I found that current flows +/- and not vice versa .. it opens but doesn't close the flap.. so I believe I must focus on the hevac module.
From RR literature the recirculation push button feeds current to the motor until it reaches the full open position , once depressed it feeds the current inverting +/- until it reaches the full closed position .
do I miss something??
As far as I know as soon as the ign pos reaches pos 2, Hevac should self test positioning recirculation flap to match the push button in open position is it right?

Click to expand...

Yes you miss a lot. The motor is assembled with the flat on the drive aligned with the top of the motor case and also assembled in position on the heater box in that orientation. The gears are fitted with the arrow on the pot gear aligned with the mark on the last drive gear. Unless you know what you are doing power should NOT be applied to the motor unless it is bolted in place on the heater box. I use 7 volts to bench test travel. Pos/neg will give travel in one direction neg/pos travel in opposite direction. NEVER EVER allow the motor to travel fully in either direction unbolted from the heater box.

ok thank you for the explanation, but still have to solve the current flow from Hevac module .. it comes only +/- and not viceversa.
Curiosity, why should never travel all the way off the case? to avoid gears to worn out or some other reason?
Thank a lot

greasemonkeylab said:

ok thank you for the explanation, but still have to solve the current flow from Hevac module .. it comes only +/- and not viceversa.
Curiosity, why should never travel all the way off the case? to avoid gears to worn out or some other reason?
Thank a lot

Click to expand...

Motor NEVER travels full amount in either direction when installed to avoid stripping gears. When the travel is calibrated motor travels in both directions alternatly until flaps are on stops either way. This tells the ECU the mid point of pot travel. If the motor is assembly correctly the flaps travel to both extremes when ignition is switched on then returns to selected in use position.

do you have any idea how the ecu finds the travels end points? my question is because I I would like to understand how does it work. As there is no wire for any signal how the hell does it find the end of travel? being the voltage constant , does the Ecu sense an increment of current as end point? and further more does the ecu needs this "end point" to revert polarity?? I didn't find any video or doc , regarding the calibration philosophy.
thanks for your help.

greasemonkeylab said:

do you have any idea how the ecu finds the travels end points? my question is because I I would like to understand how does it work. As there is no wire for any signal how the hell does it find the end of travel? being the voltage constant , does the Ecu sense an increment of current as end point? and further more does the ecu needs this "end point" to revert polarity?? I didn't find any video or doc , regarding the calibration philosophy.
thanks for your help.

Click to expand...

I have explained that the motor drives the flap in each direction in turn until the flap reaches the stops and the motor stalls. The ECU notes those positions and sets a mid point position. The motor MUST be correctly assembled and fitted BEFORE power is applied.

Latest informations.. I finally got (at least I think I got) the solution or theoretically the solution. it's not the motor , it's the hevac module, here's way theory may win:

motor are thermal controlled, as it's written one's case and even more because inside the module there is a circuit coded as BTS43212 that works as power switch with thermal cut out capabilities.
polarity reverse is done by another circuit coded L272M (total of three) that works as
Inverting Amplifier:


The circuit shown above is an inverting amplifier with the Non inverting input connected to the ground. Two resistors R1 and R2 are connected in the circuit in such a fashion that R1 feeds the input signal while R2 returns the output to the Inverting input. Here when the input signal is positive the output will be negative and vice versa. The voltage change at the output relative to the input depends on the ratio of the resistors R1 and R2. R1 is selected as 1K and R2 as 10K. If the input receives 1 volt, then there will be 1 mA current through R1 and the output will have to become – 10 volts in order to supply 1 mA current through R2 and to maintain zero voltage at the Inverting input. Therefore the voltage gain is R2/R1. That is 10K/1K = 10
(this is not mine, it comes from internet.

In this case the blue arrow indicates the inverting amplifier , yellow ones are are the resistors . Now (thank you multimeter) i found the 104 gives 0.5 instead of 1 ..and this could be the reason the motor works one way..

I'll try to replace the 104 resistor and I'll let you know if it works or not.

Hi all..
i have bench tested all the recirculation system and it works, both motors goes up and down pushing the recirculation button .. I didn't reach the dead points to avoid the gear to break . Ones fitted it doesn't work (rh motor only)
I've noticed a couple of interesting things:
1) connector C245 PIN 9 (black green) and PIN 10 (white green) Voltage 7 opening -7V closing
PIN 11 (Black red) and PIN 12 (white red) Voltage -7 opening +7V closing

Now assuming that color code has a reason to be, shouldn't be the same polarity in opening and closing.??
2) attaching the motors with no gears , they keep spinning for 10-15 secs than stop without reversing (and this make sense) , but why when I tray to block them (current grows) why they don't stop and reverse?

hoping I'm not boring you !!
Ciao

I think we're in @martyuk territory.

Here' s how respond the hevac on bench test .