LittleRed Posted April 19, 2023 Share Posted April 19, 2023 Greetings! I have an 89 and I am having trouble with my blower motor. I have low speed but my high speed is not very high. I have checked the voltage of the signal going to blower control module and it seems to be in spec for both speeds. I have replaced both the blower control module and the blower. The fault seems to be with the control module (even though it is new) but before I go and spend another chunk of money on another one (and from what I have been reading, they are not very reliable) I was thinking of building my own. My question is, is the signal going to the control module simply a varied voltage or is it a PWM (pulse width modulation) signal. Has anyone put an oscilloscope to it to see what it is? Thanks for any help and have a great day! Link to comment Share on other sites More sharing options...
Ronnie Posted April 19, 2023 Share Posted April 19, 2023 You might find this helpful: Reatta Owners Journal - HVAC Programmer Test Link to comment Share on other sites More sharing options...
LittleRed Posted April 19, 2023 Topic Author Share Posted April 19, 2023 Thank you so much Ronnie for your reply. I did find that and went through the testing procedure and the values all seem to be right but my high speed is not very high. That led me to believe that it was the control module but I don't want to spend another $140+ for another new one before I understand it a little more or at least can know for sure that it is the control module. Link to comment Share on other sites More sharing options...
Ronnie Posted April 19, 2023 Share Posted April 19, 2023 Did you check to see if the evaporator needed cleaning while you had the blower out? Even if the blower is working properly air flow will be redecided if the evaporator is dirty. 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 19, 2023 Topic Author Share Posted April 19, 2023 Ronnie, I appreciate so much your assistance with this and calling my attention to possible problems. I did check the evaporator and it was quite dirty. I took several hours to clean it out so that does not seem to be the problem. I do welcome any and all ideas as to what it could be. I am stumped. Link to comment Share on other sites More sharing options...
2seater Posted April 19, 2023 Share Posted April 19, 2023 Does the blower respond with more speed if you hotwire it directly? 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 19, 2023 Topic Author Share Posted April 19, 2023 2Seater, thank you for helping out and yes it does blow at high speed with direct 12v Link to comment Share on other sites More sharing options...
2seater Posted April 19, 2023 Share Posted April 19, 2023 (edited) I hesitate to suggest much in this area as I do not have an 89 FSM, but a scan of my 1990 FSM suggests checking the control module red/black (2B) input wire for full battery voltage. It is fed by a fusible link which is hot at all times. I don't find a specified output voltage for high speed in the FSM, but there is an orange feedback connection between the purple blower motor wire and terminal "P" of the programmer which is under the right side of the dash. I would guess that is where the programmer determines if commanded voltage is equal to actual voltage. It also says the command from the programmer to the blower module is a variable voltage. I do not know if there is a blower fan override or output control in the BCM diagnostics or not. Some functionality is different between the touch screen cars and the non. The BCM is the master controller here. In my FSM, only two conditions have a diagnostic tree: high speed fan only, or no fan operation at all 😖 Edited April 19, 2023 by 2seater 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 20, 2023 Topic Author Share Posted April 20, 2023 Hi 2seater! While the colors are different, the wires are there and active. I have the manual for the 89 and the trouble shooting is much the same. And as you said, there is no trouble shooting guide for no high blower. There is no override through the system or BCM diagnostics. I could run a switch into the car and "hot wire" but I am not ready to give it up yet, I am hoping for a better solution. Thanks for your help and guidance. Link to comment Share on other sites More sharing options...
Ronnie Posted April 20, 2023 Share Posted April 20, 2023 Have you done the programmer test I recommended above? If so what results did you get? Link to comment Share on other sites More sharing options...
LittleRed Posted April 20, 2023 Topic Author Share Posted April 20, 2023 Ronnie, I did it over the course of several weeks. My results were always similar. Fan off-0.08v fan low-8.05v fan high-9.58v. That seems to be in specs for the programer. It leads me to believe that it is the module but mine is new and it is hard to believe that it is the problem and I don't want to buy another one to try and find out. That is why I was wondering what the signal is like coming from the programer. Thanks again for helping! Link to comment Share on other sites More sharing options...
Ronnie Posted April 20, 2023 Share Posted April 20, 2023 54 minutes ago, LittleRed said: It leads me to believe that it is the module but mine is new and it is hard to believe that it is the problem and I don't want to buy another one to try and find out. Go to a salvage yard and get a good used one. Most of the big GM cars of that time period with auto HVAC controls used the same module so they should be plentiful and cheap. If that fixes the problem send the new one back. 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 20, 2023 Topic Author Share Posted April 20, 2023 Ronnie, I thank you for your advice. That looks to be the best way to go. Thanks again for all your assistance! 1 Link to comment Share on other sites More sharing options...
2seater Posted April 20, 2023 Share Posted April 20, 2023 (edited) 3 hours ago, LittleRed said: Ronnie, I did it over the course of several weeks. My results were always similar. Fan off-0.08v fan low-8.05v fan high-9.58v. That seems to be in specs for the programer. It leads me to believe that it is the module but mine is new and it is hard to believe that it is the problem and I don't want to buy another one to try and find out. That is why I was wondering what the signal is like coming from the programer. Thanks again for helping! I would guess the system is working as expected since actual on car testing is so similar. To an old school guy like me, it does appear very different than the way heater fans worked in the past. It seems the voltage split of 1.5 volts from low to high speed is pretty narrow and high speed is a full four volts or so below nominal system voltage, so the maximum speed possible would be wildly different. I don't see much of anything in the FSM that contradicts the present operating parameters? Have any probes been done of input voltage with the blower under load and operating? It seems counterintuitive that voltage would be higher under load but is it possible the system limits open circuit voltage for some reason?? Lack of feedback connection? Edited April 20, 2023 by 2seater 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 21, 2023 Topic Author Share Posted April 21, 2023 My only thought in the voltage thing is that if they are using PWM (pulse width modulation) then the voltage would not change much only the pulses. As the pulses get closer together then the voltage reading would also rise a small amount. However, I don't have an oscilloscope to confirm the presence of a pulsed signal. It would make the most sense given the circuit. Link to comment Share on other sites More sharing options...
Ronnie Posted April 21, 2023 Share Posted April 21, 2023 I don't believe the voltage coming from the programmer in the tests you did is the voltage the blower motor is getting. That voltage is telling the blower control module what to do. The blower control module has a separate 12 volt power supply and it feeds a variable voltage to the blower motor based on the signal it gets from the programmer. Link to comment Share on other sites More sharing options...
2seater Posted April 21, 2023 Share Posted April 21, 2023 Perhaps I misunderstood as well. I thought the output from the blower module to the motor was being measured? I guess it should have been obvious with the plug disconnected and probed it could only be the input to the module😖 The FSM states it is a variable voltage control signal to the module but ???? Many VOM's have a frequency setting but I don't know if that would pick the pulse width mentioned? Link to comment Share on other sites More sharing options...
Ronnie Posted April 21, 2023 Share Posted April 21, 2023 The later models might be different but below is what the '89 FSM has to say about how power is supplied to the blower motor. I -think?- it supports what I said in my last post if I stated the point I was trying to make in a way that makes sense. 1 Link to comment Share on other sites More sharing options...
LittleRed Posted April 21, 2023 Topic Author Share Posted April 21, 2023 A PWM circuit uses a low current pulsed signal which is fed into a MOSFET circuit which pulses the high current to the motor. DC motors don't like to run at low voltages. As 2seater noted, in the old days, they would use a bank of resistors to select the voltage going to the motor. This has a limited range of speed, was hard on the motor and created a lot of heat in those resistors. With the PWM, the motor always gets 12v but it is pulsed on and off quickly, so the longer the pulse timing, the slower the motor runs. It also gives one a wide range of speed. As noted, the voltage difference between low and high is not enough to make a great volume difference. Also, 9v is no where near what the max could or should be. I don't know where that leaves us. Link to comment Share on other sites More sharing options...
2seater Posted April 21, 2023 Share Posted April 21, 2023 1 hour ago, LittleRed said: A PWM circuit uses a low current pulsed signal which is fed into a MOSFET circuit which pulses the high current to the motor. DC motors don't like to run at low voltages. As 2seater noted, in the old days, they would use a bank of resistors to select the voltage going to the motor. This has a limited range of speed, was hard on the motor and created a lot of heat in those resistors. With the PWM, the motor always gets 12v but it is pulsed on and off quickly, so the longer the pulse timing, the slower the motor runs. It also gives one a wide range of speed. As noted, the voltage difference between low and high is not enough to make a great volume difference. Also, 9v is no where near what the max could or should be. I don't know where that leaves us. I know I made the error in understanding the voltages in Ronnies tutorial were to the blower motor. In reality, they are control signals TO the blower module and have no direct linear relationship to the output of the module to the motor. It is described nicely in the text from the '89 FSM. It would seem that if the control system is working as expected but the output is not as expected, the blower module is at fault. Since there are voltages given in the text, a test of the voltage received at the motor would tell the tale if there is a fault in the blower module. Link to comment Share on other sites More sharing options...
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