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AC fan speed control circuit?
Who knows where and what (coil sens therm) in picture, Is it a manual switch or what the description says switch S.P.D.T. (single pool double throw) And Drivers Heater Fan speed module box or what where is it at??
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5 Replies
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Found black metal box 4inches X 8 inches found it far right behind lower dash panel that comes off, down by round passenger vent
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This box controls the Drivers AC Fans below the heater coil and evaporator. It is protected by and internal fuse. When you turn the dial on you fan speed control it is going through this box.
This is a rare and expensive component. When I bought the my bus one of the Drivers AC fans went out because of broken heater hose flooded it. It also took out the board in this box. Putting the passenger side fan in is a PITA, the drivers side impossible.
When I put new fan in bus I added 5 AMP fuse to each of the positive wires on the two fans going to this box. You can tell if the box is getting power by just turning ignition key to accessory position, turn AC switch to on, and then turn your rheostat control and listen for a click happening where box is at. There are two large relays that control these fans. Blow this box and your looking at $7000 to $9000 from Prevost if they even have one. here are picture of the box internals
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Hi Ed my buddy has a 2000 featherlite that he has had only for a couple of months and he already replaced the fan control knob assembly but it does the same thing, turn the fan control knob and it goes full speed all the time. Prevost does have it but it is $1132.78 wow. I wonder if it could be repaired? Do you still have old box?
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You must fix the speed controller if you want to benefit from it. When mine failed it fails at one speed. Still blows but no variable speed. Which is why I solder in two fuses at motors to protect the board.
Ouch at $1,100 dollars. Find a good tech they be might be able to troubleshoot at less cost. This board does several things besides speed control for drivers air (small Ac System). I kept old board as someday I will figure it out with help of qualified tech. I have seen this board appear on ebay. Buyer beware.
The fan control knob is also an expensive Prevost part. It would be the first place I would look to see if it is bad. The Drivers AC evaportor was made by Carrier. I have the Carrier drawings. But carrier did not make the fan control rheostat or fan speed controller. Find that vendor and you may have well have discovered the lost Apache Gold.
On recent trip blowers stop working. Turnout the PAX side fuse blew that I wired in. Replaced it with new and system was back up and running. Tells me PAX side fan is master.
This controller could be fix if someone set up a breadboard test rig. I would first check the fuse on the board. Fuse looks like it is ceramic BUSE type fuse.
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These are not very complex boards. A qualified electronics tech should be able to troubleshoot.
Some common failure areas are
1- Broken solder joints. Check for minute cracks and reflow solder to fix. Vibration is usually the cause. Make sure cables are properly supported.
2- Electrolytic capacitors have a limited life span. Check for discoloration and discharge. You can test cap by desoldering one leg.
3- Relays if present can stick or have bad contact points.
4- The output drivers can short out. Not too difficult to replace if you have a soldering iron.
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