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Discussion Starter · #1 · (Edited)
Hello:

I know this has been addressed here before but none of the solutions cover mine. I have a 2000 RR SE 4.0L. The RH blower motor runs only on high. I have moved relays, checked the fuse box for short, bought a new blower motor. Relays do not help or hurt other circuits, fuse box is clean, and the new motor does exactly the same thing the old one does. The control module knob properly changes speed of the left motor. On the wire harness, the T-4 has 12v and does not change. Would like to know how to test the other wire terminals for voltage or resistance, whatever the reading should be. I have the RR repair manual and it gives non of these specs, only a diagram. The open book does appear on the display and I live over 200 miles from a dealer with the testbook to read it. Can the control module control one motor and still be faulty as to the other motor? Or does the module control both in unison? Anyone know these readings or what the problem might be? Thank You.

BW
 

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Hi, the blower units have permannent 12V feed and the motor's speed is managed on the earth path separately for each motor, it's a PWM signal and you need oscilloscope to make measurements though as long as you ruled out the blower unit which has the high speed relay incorporated it's very possible that the HEVAC ECU or the wiring to the blower unit to be at fault(i presume that being SE it's with aircon isnt it?)

download this document https://www.dropbox.com/s/1gb686ge8...ting Manual (LRL0329ENG 5th Edition).pdf?dl=0 , if you know how to use it you have the circuit diagram, the connector views and wire colours and you can compare the RH and LH inputs to the blower units or make continuity test on wires between the ECU and unit
 

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Discussion Starter · #3 ·
Hi:

Sorry, I knew I would leave something out. It does indeed have AC. I do have the wiring diagram but electrical is not my strong point. I was hoping not to have to take the other side apart but that is probably the best idea to get values at the connector to compare. Thank You.

BW
 

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Don't you have a fellow with similar vehicle to swap the HEVAC control unit for test cos it's plug and play, this coulkd save you from a lot of hassle
 

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Actually you can compare the command to the blowers at the ECU, i attached you the relevant pics, if you can't reach the pins with the multimeter probe insert thin needles and measure on those, so at connector C0791 across pins 1-2 is the output for RH blower and pins 4-5 for LH, measure on those and compare, in the right side of the connector pin layout you have the wire colours for each pin, they are described in the introduction of that document, double check for colours to not mix things there, if the outputs are similar with the same setting for both sides it means it's a wiring issue between this plug and the blower and if they are different the problem is with the controll unit.
 

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Discussion Starter · #6 ·
Hi sierrafery:

The pic of the unit itself is not the same as mine. The other C0791 diagram is correct and I found the circuit diagram in the manual that I have. 1-2 has no reading, no matter where the speed control knob is. 4-5 has a reading that rises and falls with the speed control knob. This leaves the problem to be in the ECU/ATC unit then, would that sound correct to you also? Thanks.

BW
 

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Yes, it seems that the control unit doesnt deliver for that blower and in this case only the high speed relay kicks in cos it gets direct feed on other pin keeping the blower on full speed
 
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