Heater control valve Servo Motor

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fj40toycruiser

fj40toycruiser

10 Year 15 Year
Joined
Oct 17, 2009
Threads
60
Messages
244
Location
South Central NH
New to the family 1993 fzj80. I am in the process of diagnosing why I have no front heat. I have a solid temp reading on the dash. With the cable disconnected at the firewall the valve feels to move freely. When I removed the radio and disconnected the cable at the servo motor the cable moves freely. I cannot get the servo motor to move by itself. I tested my temp control using an ohm meter and sliding the temp back & forth and determined it seems to be functioning properly. So that points to the servo motor that controls the movement of the cable..... looks like a nightmare to get to to remove. Anyone ever remove the servo motor without pulling the heater core out? Is there a way to apply 12v to the motor to see if it move when power is applied?
 
So instead of trying to remove the dashboard and get to this air mix servo I'm going to do more tests. I would like to apply 12V to the servo motor and see if it responds but I am not sure it is as easy as that. I have read in the manual

"When the temp. control lever is moved to the 'hot' side, the A/c system amplifier operates the same as for the 'cool' operation, so the current flows from Terminal 1 (Y-R) of the A/C system amplifier to Terminal 4 of the Air Mix control servo motor --> Terminal 5 (Y-G) --> Terminal 6 of the A/C system amplifier, changing the moto to the "hot' side. When the voltage of the potentiometer and the voltage of the temp control lever are the same, power to the motor is cut off.."

But I am too electrically stupid to understand exactly what that means to test the motor. Can anyone shed some light on the testing of the circuit.
 
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Based on no response I am going to apply +12V to terminal 4 of the air mix servo motor and connect the ground to terminal 5 of the servo motor to see if it responds. I am not sure if a voltage needs to be applied to terminals 1& 3 for the circuit to work. Kinda hard to believe no one has had to troubleshoot this????
 
A bi-polar stepper or servo motor should have 4 wires, two for each pole. Each pole needs to be enerized at a frequency 180 degrees from the other in a square wave or sawtooth signal. Applying 12vdc to one pole will make it move one step, probably about 1 degree depending on how it's wired.

What I'm getting at here is that you need a bi-polar stepper motor driver to make it turn like a "normal" motor would. I advise against applying anything other than the correct type of signal.

Can you post a picture of the motor and leads?
 
I can post better tomorrow from a PC. I can show you the wiring diagram,connector, and circuit function description if that helps I can also show you the pin out of the connector connected to the motor. However the motor sits on top of the heater core buried under the dash behind the radio. Very difficult to see but I will do what I can. Thank you for the response!
 
You are trying to trick the controller into thinking the motor needs to move, without knowing what's broken that could prove fruitless even if you do feed it the right signal. If the motor isn't geared you should be able to move it by hand with the power off. When the power is on the holding current from the controller acts a a brake. Have you tried to turn it with the power off?

Your would to need to power the motor directly if you want it to move without the stock controller. Connect this Qianson Simple Stepper Motor Drive Controller Reversing Speed Control Pulse Signal Generator PWM Driver Regulator: Amazon.com: Industrial & Scientific to this SainSmart CNC Micro-Stepping Stepper Motor Driver 2M542 Bi-polar 2phase 4.2A Switch: Electric Fan Motors: Amazon.com: Industrial & Scientific and get a test motor like this Qunqi NEMA17 Stepper Motor bipolar 4 leads 40mm 1.5A 39Ncm - - Amazon.com if you want to hard wire it.
 
I'm not as well versed with servo motors but it appears much simpler. You very well may be able to do what you proposed without issue. Try it with a 9volt battery first and see if it tries to turn. That should minimize the danger in frying anything. Normally they are driven with PWM signals so try tapping the voltage on and off to simulate that condition. Attempt at your own risk!

I am surprised no one on mud has dealt with this before...
 
superjuice said:
I am surprised no one on mud has dealt with this before...
Click to expand...

Me too. I am thinking if I can verify output voltage at the A/C amplifier then I can confirm that the air mix servo motor is getting juice and it is fried? The factory EWD describes the A/C amplifier as being behind the glove box door however it also indicates there is an "A/C System Amplifier" behind the radio. I will take a pic later but I can see what appears to be this "A/C System Amplifier" connector as shown in the EWD but I do not see said "A/C System Amplifier". Anyone have experience with this "A/C System Amplifier" behind the radio that can describe its physical appearance/location. If that is part of this circuit and is not present on my set-up perhaps that is the root cause of my problem. I can see the AC amplifier behind the glove box and I will check that but the "A/C System Amplifier" seems to be non-existent. FWIW I am using 1996 EWD but I am under the impression the HVAC system and its controls didn't change from 93-96 it only changed when they offered the Auto climate control in 97 on LX's, Anniversary, & Collectors Edition.

When I removed the cable at the servo motor I could not easily move that pivot point and I didn't want to damage the motor trying to move the pivot point if it was fine but the thought did cross my mind because I couldn't move it that it was seized. I will check that too ensuring there is no power to it i.e. key off condition.

Thanks for the help so far for you that have chimed in!
 
Hi all:

New member, long time lurker.

I have the "heater won't shut off problem." Finally got the dash apart enough to find the servo. Moving just fine. No action on the cable to the heater valve, though. After much poking and some colorful language, I found the busted end of the cable on the little shaft that engages it.

Surprised, as many have said, that this hasn't been seen much. Here's what I know.

Cable end is broken off at the servo end. It does not attach near (or visibly near) the servo, rather, it's found via the glove box. Squeezed the glove box together so it would flop down and give access to the center of the console, reached up and over (to tight even to get a mirror in) and found the end of the cable, broken off and can feel the cable "sheath" and it's anchor point.

Questions for the group:

- Anyone ever change this pesky little dog of a cable?
- Anyone know the part number of a new one? Haven't been to my dealer yet, but will try that.
- Can it be changed without pulling the dash structure completely out of the car? I can't see where the cable comes through the firewall at all.

All suggestions taken!

Bill

'94 FZJ80 "Mean Green" 245L
'02 FZJ105 "Moby" 165K
'08 Hybrid Highlander "Hiram the HyHi" 110K
'12 FJ Cruiser "Blu-cifer" 35K
... and
'66 Jeep CJ6 "Percy the Persimmon Jeep" 67K
'08 Roadtrek Agile SS (Freightiner Sprinter RV) "Beluga the white whale" 80K
'83 Porsche Cab "Pepe le Porsche" a.k.a. "the road oiler" 51K
2000 and 2005 Vespa Scooters "Hop and Skip" <who knows>k
'60 Beechcraft Bonanza - "<no name>" too-many-to-count-K
... too many toys * all for sale * 'cept the 3 cruisers, of course...
 
Bill J said:
Hi all:

New member, long time lurker.

I have the "heater won't shut off problem." Finally got the dash apart enough to find the servo. Moving just fine. No action on the cable to the heater valve, though. After much poking and some colorful language, I found the busted end of the cable on the little shaft that engages it.

Surprised, as many have said, that this hasn't been seen much. Here's what I know.

Cable end is broken off at the servo end. It does not attach near (or visibly near) the servo, rather, it's found via the glove box. Squeezed the glove box together so it would flop down and give access to the center of the console, reached up and over (to tight even to get a mirror in) and found the end of the cable, broken off and can feel the cable "sheath" and it's anchor point.

Questions for the group:

- Anyone ever change this pesky little dog of a cable?
- Anyone know the part number of a new one? Haven't been to my dealer yet, but will try that.
- Can it be changed without pulling the dash structure completely out of the car? I can't see where the cable comes through the firewall at all.

All suggestions taken!

Bill

'94 FZJ80 "Mean Green" 245L
'02 FZJ105 "Moby" 165K
'08 Hybrid Highlander "Hiram the HyHi" 110K
'12 FJ Cruiser "Blu-cifer" 35K
... and
'66 Jeep CJ6 "Percy the Persimmon Jeep" 67K
'08 Roadtrek Agile SS (Freightiner Sprinter RV) "Beluga the white whale" 80K
'83 Porsche Cab "Pepe le Porsche" a.k.a. "the road oiler" 51K
2000 and 2005 Vespa Scooters "Hop and Skip" <who knows>k
'60 Beechcraft Bonanza - "<no name>" too-many-to-count-K
... too many toys * all for sale * 'cept the 3 cruisers, of course...
Click to expand...
well what happened??
 
Bumping this thread. I've been searching but I've had no luck finding the [part number for the servo-control motor for the heater valve. Anyone?

I've found this 87161-060020 which is amplifier, heater servo motor ( whatever this is) doesn't seem to be a new servo
 
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Another bump. My issue is that I do not have a linear relationship between temperature slider and actual heat - it’s either on or off, but the heat I do have is great. I’m not having any other issues and have verified that servo, cable, valve (relatively new) are all working. No erratic behavior either.

The “switch” (on/off) appears to be right at the 85° mark. I’ve taken the dash apart multiple times for different reasons (lights), have visually watched the motor operate, etc. Would be nice to be able to run heater in the middle when it’s not cold enough for full heat.

This is the one thread I came across that seems like it could be related, since I have checked everything else. So, am I correct in thinking that, given my symptoms and what I have checked, I am either having a connection issue in the blue plug or one of the little soldered pins on the back of the climate control box, thus incorrect/no blend door action?
 
Bump (sorry). I’m sure I could try it, just like understanding

Sending out the forum bat signal

:flipoff2::flipoff2::flipoff2:
 
I had the exact issue the OP had. Looked Up this thread before I fixed it, so I thought I would circle back and give it an update. My issue ended up being the amplifier for the servo motor. Luckily I had the dash already out and an extra servo motor and amplifier on the shelf so I was able to swap parts to test and see what the issue was.

On my 95 the part number was:
87161-60020

It is located to the left of the climate control box near the driver right knee behind the dash.
 
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