Troubleshooting My Manual Climate Control (All I Get Is Hot Air)
02-09-2015, 08:01 PM
#1
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Troubleshooting My Manual Climate Control (All I Get Is Hot Air)
I have a 1999 Maxima with manual climate control and it blows hot air all the time regardless of the temperature setting. The motor doesn't turn so I went through the troubleshoot in Section HA of the FSM.
I got to the check for the push control unit shown on page HA-51. When I check the voltage between pins 22 and 23, I get 10 volts as I slide the temp lever from HOT-COLD and COLD-HOT which sounds correct. However, I also get 10 volts at the HOT stop and the COLD stop when I'm not sliding the temp lever. The FSM says I should get 0 volts here so I'm guessing that the control unit itself is bad.
Am I interpreting this correctly?
I have the air mix door motor out so is there a quick check I can make on the motor to make sure it's OK.
Thanks for your help (again)
I got to the check for the push control unit shown on page HA-51. When I check the voltage between pins 22 and 23, I get 10 volts as I slide the temp lever from HOT-COLD and COLD-HOT which sounds correct. However, I also get 10 volts at the HOT stop and the COLD stop when I'm not sliding the temp lever. The FSM says I should get 0 volts here so I'm guessing that the control unit itself is bad.
Am I interpreting this correctly?
I have the air mix door motor out so is there a quick check I can make on the motor to make sure it's OK.
Thanks for your help (again)
02-09-2015, 10:32 PM
#2
I had a problem in my 97 with the heat always being on high. I followed the manual troubleshooting section and came up with a bad control unit. Got a junkyard replacement and put it in. Control unit didn't fix the problem. Re-did the troubleshooting and I got different results pointing at the motor. The point I'm trying to make is that it is easy to screw up the diagnosing. Replaced the motor and life was good once again.
How can you check the motor to see if it is good. I don't know. The mode door motor is more than just a simple motor. When you tested pins 22 & 23, you were testing the voltage going to the motor. You could jumper 12 volts to those pins, say +12 on pin 22 and ground on pin 23, and the motor should turn in one direction. Then reverse the connections and the motor should turn in the opposite direction.
But because of the PBR resistor built into the motor, the actual motor is probably good. The PBR resistor is sending a bad signal to the push control unit. The FSM talks about checking resistance of the PBR (page HA-57) but there is no useful information other than pin numbers. It doesn't tell you what resistance to expect. In fact, if you follow those directions as printed, you stand a good chance of burning out your meter. They forgot the step where you turn off the power before measuring resistance. You NEVER measure resistance with power on.
I have not done this, but if you measure the voltage coming from the PRB to the control unit on pin 26 of the push unit, you should see a changing voltage IF the motor was working. I don't know what the voltage should be, but I doubt if it would get as high as 12 volts.
The fact that you has 10 volts on pins 22 & 23 when you should have had 0, makes me think that the PBR is sending a voltage that is in effect telling the motor to constantly run.
The air mix door motor has some sliding contacts inside it that are part of the PBR circuit. In my case, these sliding contacts were the problem. They had developed corrosion and were not making contact.
Here is the Air Mix Door Motor opened up. In the left half, about the middle towards the bottom, is a small gear by itself. It is mounted on the PBR and makes it turn. If you look at the right half, there is a white half gear that has some metal fingers on it. The metal is copper and you can see green corrosion on the fingers. That corrosion is why my motor stopped working.
If you could clean the copper fingers and bend the fingers a tiny bit more, you would be good to go.
But when you take the motor apart, you have to be aware of the strange construction.
When I just pulled the motor apart, most of the gears fell out because the half moon gear is underneath 2 of the 3 gears in the top left of the photo above. There is a definite alignment so that the motor stops at the end of the travel and reverses direction. If I remember correctly, the 2 halves of the motor did not want to separate easily because of the gears being sandwiched (which I didn't know at the time), so I used brute strength and ignorance to separate the halves and then had to pick up all the gears.
Maybe if you just separate the halves slightly and then stick something thin and flat in to hold the half moon gear, you might be able to hold the half moon gear in the position it needs to be in.
How can you check the motor to see if it is good. I don't know. The mode door motor is more than just a simple motor. When you tested pins 22 & 23, you were testing the voltage going to the motor. You could jumper 12 volts to those pins, say +12 on pin 22 and ground on pin 23, and the motor should turn in one direction. Then reverse the connections and the motor should turn in the opposite direction.
But because of the PBR resistor built into the motor, the actual motor is probably good. The PBR resistor is sending a bad signal to the push control unit. The FSM talks about checking resistance of the PBR (page HA-57) but there is no useful information other than pin numbers. It doesn't tell you what resistance to expect. In fact, if you follow those directions as printed, you stand a good chance of burning out your meter. They forgot the step where you turn off the power before measuring resistance. You NEVER measure resistance with power on.
I have not done this, but if you measure the voltage coming from the PRB to the control unit on pin 26 of the push unit, you should see a changing voltage IF the motor was working. I don't know what the voltage should be, but I doubt if it would get as high as 12 volts.
The fact that you has 10 volts on pins 22 & 23 when you should have had 0, makes me think that the PBR is sending a voltage that is in effect telling the motor to constantly run.
The air mix door motor has some sliding contacts inside it that are part of the PBR circuit. In my case, these sliding contacts were the problem. They had developed corrosion and were not making contact.
Here is the Air Mix Door Motor opened up. In the left half, about the middle towards the bottom, is a small gear by itself. It is mounted on the PBR and makes it turn. If you look at the right half, there is a white half gear that has some metal fingers on it. The metal is copper and you can see green corrosion on the fingers. That corrosion is why my motor stopped working.
If you could clean the copper fingers and bend the fingers a tiny bit more, you would be good to go.
But when you take the motor apart, you have to be aware of the strange construction.
When I just pulled the motor apart, most of the gears fell out because the half moon gear is underneath 2 of the 3 gears in the top left of the photo above. There is a definite alignment so that the motor stops at the end of the travel and reverses direction. If I remember correctly, the 2 halves of the motor did not want to separate easily because of the gears being sandwiched (which I didn't know at the time), so I used brute strength and ignorance to separate the halves and then had to pick up all the gears.
Maybe if you just separate the halves slightly and then stick something thin and flat in to hold the half moon gear, you might be able to hold the half moon gear in the position it needs to be in.
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ballerchris510
3rd Generation Maxima (1989-1994)
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09-10-2015 09:35 PM