Defrost fan rehab and rebuild thread (fresh air fan), or How the heck do if fix this thing? |
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Defrost fan rehab and rebuild thread (fresh air fan), or How the heck do if fix this thing? |
DRPHIL914 |
Jan 21 2021, 08:55 AM
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#1
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
I have been dealing with this for 12 years, a non-running defrost fan. i even pulled this out 2 years ago and rebuilt it with new flapper seals and main body seal then made sure fan turned but didnt bench test the motor or resisitors, so as a result it still does not work properly. i will be documenting this because 914rubber and Mark will soon be putting together a kit for this that includes all the hardware seals and even a motor i believe, BUT i still have problems and questions!!! so i am starting this thread to get information on diagnosing the common causes of it not working and how to fix it, and then document the rebuild and replacement of the motor, fan, resistor and maybe the control unit in dash. Others have documented the reinstallation of the fan and the cables so i will not duplicate that. and we may want to link other threads hear that have done that as well.
Mark is sending me a kit soon, so while i wait for it, i will have to get some more information about the wiring and resistors function and how to test them . I had this out last week and tested 3 different control units due to thinking that my issue was a control issue, because it runs on one speed, #2, and anything else does not work and it will then throw the fuse. most assume this would be caused by bad slider unit but i tested 3 of them and 2 are like new with no wear on the sliders , still same result. so i am suspecting the resistors /plug aparatus . If anyone has done this and cares to share how to examine and test that for proper function, lets start there. Resistor function, which lead is which and examination of the control units I will take pictures of mine tonight and post those soon. once this figured out and fixed i will do a full step bystep on reassembly too. Looking for lots of help and input on this, thanks!!! Dr. Phil |
Superhawk996 |
Jan 25 2021, 07:38 AM
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#2
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914 Guru Group: Members Posts: 5,815 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
@DRPHIL914
I'm going to pick one more snippet from your quote. Not trying to beat up on you personally, but, it speaks to Rule #2. If I'm making you mad by picking out snippets, I'll stop, just let me know. However, it illustrates how I got to the rules we started with. " . . . the resistance values seemed strange to me to, was trying to figure out how it would fail that way." This is why a good schematic is a must have. Depending on the complexity of the system, It can be hard, if not impossible troubleshoot effectively without a schematic. Good schematic from Haynes. B&W is a bit more work to read for color codes but all info is available. The schematic explains the switches, their normal position, and their operation. Nice for color codes, but, a block diagram is useless for this type of troubleshooting. Explains nothing other than the colors of the wire. |
DRPHIL914 |
Jan 25 2021, 08:09 AM
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#3
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
@DRPHIL914 I'm going to pick one more snippet from your quote. Not trying to beat up on you personally, but, it speaks to Rule #2. If I'm making you mad by picking out snippets, I'll stop, just let me know. However, it illustrates how I got to the rules we started with. " . . . the resistance values seemed strange to me to, was trying to figure out how it would fail that way." This is why a good schematic is a must have. Depending on the complexity of the system, It can be hard, if not impossible troubleshoot effectively without a schematic. Good schematic from Haynes. B&W is a bit more work to read for color codes but all info is available. The schematic explains the switches, their normal position, and their operation. Nice for color codes, but, a block diagram is useless for this type of troubleshooting. Explains nothing other than the colors of the wire. no, please i appreciate the info, and being educated! help me understand the basics like being able to read the schematics will help me trouble shoot other issues in the future, so the M is the motor correct, and #3 high does not go thru either of the resistors, just the bimetalic plate? if the plate were not conducting current you would not get the fan to run on that setting and resistance with be infinity(short?) |
Superhawk996 |
Jan 25 2021, 08:25 AM
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#4
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914 Guru Group: Members Posts: 5,815 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
@DRPHIL914
so the M is the motor correct -- Yes, Correct and #3 high does not go thru either of the resistors -- Correct . . if the plate were not conducting current you would not get the fan to run on that setting -- can't really answer that question without a physical inspection of the assembly. I tried to look at BeatNavy's photos and I still can't tell for sure. However, I can see from the photo the plate is basically a thick, solid copper trace. The chance of that opening up is slim to none. The amount of current it would take to melt that open would have melted the external wiring 1st. I think I might be misunderstanding the question. Let's call the switches; bi-metallics switches. What I'm calling the plate is the structure that the reistors and the bi-metallic switches are attached to. So when a bi-metallic switch is normally open you would read the resistance of the Motor + the resistor. When the bi-metallic switch is closed (should only be when the resistor is over heating), the bi-metallic switch deforms to the closed position, and bypasses the resistor with a short (zero ohm) connection, and the motor would run in high speed (just like position #3), the fan should pull more air across the resistor, cool it down, and then the bi-metallic switch should return to the normally open position and the fan would return to its regulated speed. If the bi-metallic switch were permanently deformed to be normaly closed (even when cool) then you would read the motor resistance only just like you would in position #3. and resistance with be infinity(short?) -- A short = 0 ohms, open circuit = infinity. Since you are reading 0.8 ohm on all three speeds, we know the plate is not open and, that we have conductivity between all three potential current paths though the motor Adding on: Around each resistor, you see a switch that operates as a square wave. Either OFF or ON. When that switch closes, you have a short around the wire wound resistor. Therefore, you would only read the motor winding resistance when measuring though the switch if this switch were closed. These are the bi-metallic switches that are located blow the resitors in Brent's photo. Note: DMM's can have 0.1- 0.3 ohm of resistance just in the leads (especially if using add-on's like alligator clips. My cheap DMM reads 0.2 ohms with a dead short and alligator clips attached. So moral of the story is your ohm readings may differ slightly and/or a dead short may still show as 0.2 ohms or so. |
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