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Old 05-31-2015, 08:35 PM   #1
RHR
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Help with AC blower

I have an '08 Damon on a Ford F-53 chassis. My AC unit is an Acme, and the blower is a 4 speed, which does not work on high. The lower 3 speeds all work fine. I can't seem to find much info as they (Acme) are apparently no longer in business. I checked the switch and find voltage coming from the switch on high, and voltage to the resistor on high. I believe there is a relay on this unit for high fan speed also. Is there a way to verify if the resistor is bad, and does anyone know if the relay is before the resistor or after? I am trying to make the repair before an upcoming trip. The unit is cool, not real cold either, but I have yet to check the charge level.
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Old 05-31-2015, 09:39 PM   #2
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I can't give you specifics on your coach, but generally the power to the motor on high doesn't run through the resistor block. It's generally a straight shot from either a fuse or a relay. Big current on that wire when it's on high, so good chance for melted or overheated connector somewhere in that circuit, as well as fuse and/or relay issues.

Sometimes, the easiest way to find those components is to work backwards, towards the power source, starting at the blower motor.
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Old 05-31-2015, 10:06 PM   #3
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All speeds run through the resistor in one way or another, they usually melt the plug. All the motorhomes I have worked on had Evens/Tempcon units and used a Ford resistor, not sure about Acme but you could pull it and find a part number.

Here is a diagram of a Tempcon unit, may help.

electrical_schematics.pdf
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Old 06-01-2015, 06:59 AM   #4
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I'm looking at that wiring diagram, and the high speed (orange) wire does not appear to be running through that resistor block.

If the blower speeds other than high all work, that resistor block is fine. You could also fairly assume that the 12v wire supplying power to the blower switch is also good - also because the lower speeds are fine.

This leaves the power between the speed selector switch "high" position, and the blower motor in question. As mentioned, it's very possible that circuit will have a relay in it. If so, the "high" wire (orange in the diagram) will control a relay, relieving that speed control switch of the rather high loads required to supply that blower motor.

The relay (if equipped) will have it's own power supply, often fused, but maybe an auto reset (thermal) breaker. From there, it's usually a straight shot to the blower motor.
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Old 06-01-2015, 06:53 PM   #5
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Thanks for the responses so far. Connectors at switch and resistor all appear fine, not burned, melted crispy, etc. I did find a relay this evening finally buried under everything else under the dash, and I will replace it tomorrow and see if that is bad. I'm not sure if they can be checked, but the cost is pretty negligible anyway. All wiring does look in good condition from the dash control unit to the blower unit, and the fuses I could find for the AC are OK also. I was able to find a pretty old schematic for Acme someplace, but I'm not positive it would be the same although it certainly appears similar. It also looks as though the high speed also goes through the resistor on their design for some reason. It just puzzled me as I thought as others have mentioned that the high speed usually runs direct to the blower. I will post a result tomorrow if either fixes the issue. Thanks for the input.
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Old 06-01-2015, 07:59 PM   #6
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Relay, if you wanted to check it with a test light prior to replacing, should have:

1. One wire that's hot whenever the key is on.
2. A ground wire
3. The "high speed" wire coming from the switch (hot with key on and switch on high)
4. The wire to the blower motor.


My bet is that wire #1 has a blown fuse or circuit breaker
or
The relay is bad

-Al
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Old 06-09-2015, 10:26 PM   #7
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Well I traced all wiring out, no issues there as I had suspected, and no other fuses were found. Changed relay with another good one also to no avail. Ordered a new resistor, and will see if that is the solution. I guess I shouldn't complain about no high speed on the fan, after all the other 3 speeds work, lol.
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