Blend Door Motor…Test Procedure?
Thread Starter
Advanced
Joined: Jan 2006
Posts: 77
Likes: 1
Blend Door Motor…Test Procedure?
I have a 1986 Coupe with the C68 Climate Control System. I have just ordered a new Programmer because the original has too many failed electrical components on it.
I was going through and following the system test procedure in the FSM (checking voltages, resistance, etc) and came to a section that stated that I should be able to manually move the blend door motor and measure the voltage (8A-64-9, No. 6). I have removed my blend motor, and I cannot move the lever by hand. I took it apart to clean it out, and inside of it, I removed the white plastic gear. With this out, the black portion of the motor rotates freely and the coil (silver cylinder) rotates freely. BUT, when that white gear is in place it’s like it puts a bind on the gears in there and nothing moves at all.
On the blend door motor:
Resistance across Terminals C to D is 220 ohms (OK as per FSM)
Resistance across Terminals A to E is 1890 ohms (FSM wants 2000)
Am I supposed to be able to move this thing by hand? It did move while connected to the car for a brief minute. It rotated one direction, stopped, then reversed direction and then stopped, then nothing after that.
Thanks for any help!
I was going through and following the system test procedure in the FSM (checking voltages, resistance, etc) and came to a section that stated that I should be able to manually move the blend door motor and measure the voltage (8A-64-9, No. 6). I have removed my blend motor, and I cannot move the lever by hand. I took it apart to clean it out, and inside of it, I removed the white plastic gear. With this out, the black portion of the motor rotates freely and the coil (silver cylinder) rotates freely. BUT, when that white gear is in place it’s like it puts a bind on the gears in there and nothing moves at all.
On the blend door motor:
Resistance across Terminals C to D is 220 ohms (OK as per FSM)
Resistance across Terminals A to E is 1890 ohms (FSM wants 2000)
Am I supposed to be able to move this thing by hand? It did move while connected to the car for a brief minute. It rotated one direction, stopped, then reversed direction and then stopped, then nothing after that.
Thanks for any help!
Melting Slicks
Joined: Apr 2003
Posts: 3,110
Likes: 6
From: Red Sox Nation! RI
I don't remember if you can move the motor by hand or not. If you can, it will have a good amount of tension on it - it's like a stepper motor. I don't recall anything in the manual about trying to move it by hand either. There should be a couple of electrical tests that power the motor to the open and closed positions.
I know those test instructions sucked with a capital S. Maybe you read something wrong?
I know those test instructions sucked with a capital S. Maybe you read something wrong?
Thread Starter
Advanced
Joined: Jan 2006
Posts: 77
Likes: 1
I replaced the programmer (the black box above the gas pedal) and the blend door motor is working like it should. I could not move my blend door motor by hand, so I would say that the FSM's test procedure is not accurate.
To all those people out there with A/C issues (vent doors not opening and directing air like it's suppose to), it is MOST LIKELY THE PROGRAMMER that is the problem.
I bought a new NOS programmer from thepartsladi on eBay. I paid $350, but it's worth it. After all the checking I did, the blend door motor DOES NOT EXIST anywhere. I couldn't even find a used one. No dealership had the programmer either and I wouldn't trust a used one.
Hope this helps someone with a similar issue!
To all those people out there with A/C issues (vent doors not opening and directing air like it's suppose to), it is MOST LIKELY THE PROGRAMMER that is the problem.
I bought a new NOS programmer from thepartsladi on eBay. I paid $350, but it's worth it. After all the checking I did, the blend door motor DOES NOT EXIST anywhere. I couldn't even find a used one. No dealership had the programmer either and I wouldn't trust a used one.
Hope this helps someone with a similar issue!
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
I replaced the programmer (the black box above the gas pedal) and the blend door motor is working like it should. I could not move my blend door motor by hand, so I would say that the FSM's test procedure is not accurate.
To all those people out there with A/C issues (vent doors not opening and directing air like it's suppose to), it is MOST LIKELY THE PROGRAMMER that is the problem.
I bought a new NOS programmer from thepartsladi on eBay. I paid $350, but it's worth it. After all the checking I did, the blend door motor DOES NOT EXIST anywhere. I couldn't even find a used one. No dealership had the programmer either and I wouldn't trust a used one.
Hope this helps someone with a similar issue!
To all those people out there with A/C issues (vent doors not opening and directing air like it's suppose to), it is MOST LIKELY THE PROGRAMMER that is the problem.
I bought a new NOS programmer from thepartsladi on eBay. I paid $350, but it's worth it. After all the checking I did, the blend door motor DOES NOT EXIST anywhere. I couldn't even find a used one. No dealership had the programmer either and I wouldn't trust a used one.
Hope this helps someone with a similar issue!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Huh? There's nothing in either motor to keep you from moving the shaft by hand. There are differences in how they link to the Temp Door and I'd imagine those that move the door with a gear make it difficult to move much of anything - unless you remove it of course.
I do agree that the motors rarely, if ever go bad. Soaking the windings with Coolant or water would be one cause, but they're sealed up pretty tightly and some engineer was probably smart enough to realize what happens when you mix moisture with electricity. Anyway, if you want to test the motor, apply battery voltage and a ground. That should move it. Reverse the leads and it should spin the other way. And, through '89 at least, the power and ground leads are Tan/Black and Yellow. There are a couple extra wires in the Harness that do other things, so pay attention to the schematic before you start applying voltage.
Beats me what goes into a Programmer Rebuild - early models often benefit from from resistor replacement, but I'm dangerous with a soldering iron so if I needed one, I'd buy it somewhere.
I do agree that the motors rarely, if ever go bad. Soaking the windings with Coolant or water would be one cause, but they're sealed up pretty tightly and some engineer was probably smart enough to realize what happens when you mix moisture with electricity. Anyway, if you want to test the motor, apply battery voltage and a ground. That should move it. Reverse the leads and it should spin the other way. And, through '89 at least, the power and ground leads are Tan/Black and Yellow. There are a couple extra wires in the Harness that do other things, so pay attention to the schematic before you start applying voltage.
Beats me what goes into a Programmer Rebuild - early models often benefit from from resistor replacement, but I'm dangerous with a soldering iron so if I needed one, I'd buy it somewhere.
Thread Starter
Advanced
Joined: Jan 2006
Posts: 77
Likes: 1
Mine wouldn't move by hand....it felt like I was going to strip the internal gears if I kept applying pressure, so I backed off before doing any damage.
As far as a Programmer rebuild, I assume the two resistors that go bad are replaced and everything is checked for proper operation. I know when I started troubleshooting my Programmer's board, I found two defective diodes and a bad transistor. That combine with the heat damage I saw on the board was enough for me to buy a new one.
As far as a Programmer rebuild, I assume the two resistors that go bad are replaced and everything is checked for proper operation. I know when I started troubleshooting my Programmer's board, I found two defective diodes and a bad transistor. That combine with the heat damage I saw on the board was enough for me to buy a new one.
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
I had thought about doing some test procedures as well. I know on my 89, the blend door will stay all the way shut for cooling when the temp is at 60-85. Then when I turn it to 90, the door moves all the way to the other side for max heating.
Thread Starter
Advanced
Joined: Jan 2006
Posts: 77
Likes: 1
With my new Programmer in place, the blend door motor will position itself to completely block the heater core from 60 -74 degrees. Once you set the temperature for 75-85 its position varies between the two extremes. When you set it for 90, the heater core side is all the way open and hot air is all the comes out.
Before I replaced the Programmer, the blend door motor would rarely move. One time, it moved all the way one direction, stopped, then moved the other direction and never moved again after that. Now it's working like it should.
Before I replaced the Programmer, the blend door motor would rarely move. One time, it moved all the way one direction, stopped, then moved the other direction and never moved again after that. Now it's working like it should.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Drifting
Joined: Jun 2003
Posts: 1,455
Likes: 5
From: Upstate South Carolina
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
With my new Programmer in place, the blend door motor will position itself to completely block the heater core from 60 -74 degrees. Once you set the temperature for 75-85 its position varies between the two extremes. When you set it for 90, the heater core side is all the way open and hot air is all the comes out.
Before I replaced the Programmer, the blend door motor would rarely move. One time, it moved all the way one direction, stopped, then moved the other direction and never moved again after that. Now it's working like it should.
Before I replaced the Programmer, the blend door motor would rarely move. One time, it moved all the way one direction, stopped, then moved the other direction and never moved again after that. Now it's working like it should.
That is what mine does. At 90, I can't get max heating as the doors shut and feels like it is in heat mod. I never could figure out if there was something wrong, or just the way it is. I have to then set it to bi-level to get some air flow. I like my heat blowing on me. The PO replaced the entire controller a few years before I bought it, so that should be fine.
Pro
Joined: Dec 2011
Posts: 626
Likes: 15
From: Austin, TX
The problem I have with my 92 is that when I switch on my climate control (C68), no matter A/C or heater at any speed, even auto, I can listen like the air blowing but it's not coming into the car.
How can I check if the programmer is working properly? What about the blend door? Where is this second one?
Thanks in advance
How can I check if the programmer is working properly? What about the blend door? Where is this second one?
Thanks in advance
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The C68 system does a blend door calibration when you first turn on the ignition. It moves the blend door all the way open, all the way closed and then sets it to where the temperature setting on the HVAC control head says it should be. This is controlled by the combination of the HVAC control head and the HVAC programmer. The control head sends the command to move the motor to the programmer (which actually controls the motor), then the motor sends its position to the control head so the control head knows where it is.
There are gears in the motor that move the lever that controls the blend door position. There is a HUGE reduction there, so it's impossible to move the blend door lever by hand.
The HVAC system defaults to HEAT mode (it's actually required by federal law). You need to check ALL the outlets to see if air is coming out. There are TWO outlets under the dash on each side (one for heat and one for cool in bi-level mode), so check both of them.
There are gears in the motor that move the lever that controls the blend door position. There is a HUGE reduction there, so it's impossible to move the blend door lever by hand.
The HVAC system defaults to HEAT mode (it's actually required by federal law). You need to check ALL the outlets to see if air is coming out. There are TWO outlets under the dash on each side (one for heat and one for cool in bi-level mode), so check both of them.
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
iirc, i did the solder job when i first got my car 4 years ago and fixed the no heat, then over time like above posts, i would have to press bi-level to get heat and it would take forever for the doors to direct ac, when on; to where i think it should be.
i know something is wrong
i had a 85 it was manual and i wish I could just swap it over and forget all this pressing of buttons that does not do anything.
anyone ever convert an auto to manual?
i know something is wrong
i had a 85 it was manual and i wish I could just swap it over and forget all this pressing of buttons that does not do anything.
anyone ever convert an auto to manual?
Last edited by slickfx3; Nov 5, 2012 at 12:26 PM.
Pro
Joined: Dec 2011
Posts: 626
Likes: 15
From: Austin, TX
Advanced
Joined: Oct 2012
Posts: 79
Likes: 0
You are correct, the FSM walks you through a series of tests that you perform by using the head unit. Unfortunatley my test said that the programmer was bad and after I replaced it I still don't have any heat. I'm going to go thru the test again and see what it says this time.
Racer
Joined: Nov 2011
Posts: 274
Likes: 12
From: Louisburg NC
I'm not sure this applies to the '86 but here's my experience with my '94.
My heat died last March but I didn't worry about it then 'cause it was March in NC. Through the summer my A/C didn't work very well. I did a bunch of trouble shooting over the summer as time permitted. I got no codes. Now that it's cold the heat problem is becoming more urgent. I learned that you can see the blend door by removing the temperature sensor from the top of air box.
I found that it was not moving no matter what. I removed the blend door motor which allows it to be moved by hand. I now have heat.
Here's the motor.
Ugly, ain't it?
I removed the gears to allow the motor to turn freely.
Then I unplugged the motor wires from the curcuit board. I connected a 7.5VDC power supply to the motor. At first it didn't move until I spun the motor shaft with my fingers. It started spinning. I reversed the polarity on the power supply and the motor spun the opposite way.
A couple of drops of sewing machine on the bearing where the shaft comes out of the motor and put it back together.
I put it back in the car a little while ago. Works like a champ. We'll see how long it lasts. Didn't cost me 90 bucks for a new one though.
My heat died last March but I didn't worry about it then 'cause it was March in NC. Through the summer my A/C didn't work very well. I did a bunch of trouble shooting over the summer as time permitted. I got no codes. Now that it's cold the heat problem is becoming more urgent. I learned that you can see the blend door by removing the temperature sensor from the top of air box.
I found that it was not moving no matter what. I removed the blend door motor which allows it to be moved by hand. I now have heat.
Here's the motor.
Ugly, ain't it?
I removed the gears to allow the motor to turn freely.
Then I unplugged the motor wires from the curcuit board. I connected a 7.5VDC power supply to the motor. At first it didn't move until I spun the motor shaft with my fingers. It started spinning. I reversed the polarity on the power supply and the motor spun the opposite way.
A couple of drops of sewing machine on the bearing where the shaft comes out of the motor and put it back together.
I put it back in the car a little while ago. Works like a champ. We'll see how long it lasts. Didn't cost me 90 bucks for a new one though.