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Old 05-22-2016, 09:29 PM   #1
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Question on AC fan......

Actually this is in my Lance camper but a DOmetic AC is a Dometic AC.

The squirrel cage fan will not spin on any of the settings unless I take the cover off and get it spinning by hand. Then it will spin fine on any speed....until you shut it off then you have to do this again.

Is there a start capacitor for the fan...usually there is I thought on AC motors where direction of rotation is important....?

Anyone have this issue and fix it. Not wanting to replace a whole unit.

The fan does not have any binding I can feel when not powered on...spins fairly easy.
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Old 05-22-2016, 09:32 PM   #2
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Actually this is in my Lance camper but a DOmetic AC is a Dometic AC.

The squirrel cage fan will not spin on any of the settings unless I take the cover off and get it spinning by hand. Then it will spin fine on any speed....until you shut it off then you have to do this again.

Is there a start capacitor for the fan...usually there is I thought on AC motors where direction of rotation is important....?

Anyone have this issue and fix it. Not wanting to replace a whole unit.

The fan does not have any binding I can feel when not powered on...spins fairly easy.

I believe you will need a new fan motor , the start capacitor on the AC operates the compressor . not to bad a job at all anyone that can turn a screw should be able to do it , easy access
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Old 05-22-2016, 09:35 PM   #3
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Yah I thought the start cap was on the compressor...I just could not remember.

Do you know by off chance if the squirrel cage fan motors are easily ordered from Dometic...or?

I will research it tomorrow anyway. Don't need AC tonight anyway just found it not working when we set up for our daughter.

I appreciate the response.
scott
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Old 05-22-2016, 09:38 PM   #4
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The blower motor also has a capacitor. Usually it is a dual capacitor, blower motor and compressor.

Rick
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Old 05-23-2016, 08:35 AM   #5
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Yah I see that now on the schematic for the wiring. Might try just replacing that first...then the motor if that isn't it. Motor isn't bound up or feel any resistance so...we will see.
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Old 05-23-2016, 09:13 AM   #6
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Yah I see that now on the schematic for the wiring. Might try just replacing that first...then the motor if that isn't it. Motor isn't bound up or feel any resistance so...we will see.
Does your compressor start up ? if so then you'll need a new blower motor . Let us know what you find how much time it takes you and how much extra money you spend
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Old 05-23-2016, 09:39 AM   #7
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Compressor sounds like it is running normal...not like it is stuck. Usually when they don't start it is very obvious. However I need to actually take the cover back off and hand spin the blower and put it on AC and make sure the compressor is running properly and getting cold.

Will try that shortly....was not too into it last night.

I see they sell an AC kit for it with blower motor...fan..squirrel cage and cap. Probably best bet verses buying this and that and ship multiple times I suppose. Granted that the only issue is the blower.
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Old 05-23-2016, 09:55 AM   #8
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Agreed may as well do the whole kit instead of nickle and dimeing it . not uncommon for the blower motor to go bad like you describe even with a good capacitor.
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Old 05-23-2016, 10:13 AM   #9
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The compressor works....just ran the AC and it gets cold...just had to hand spin the motor.

So no big I guess. Order the motor kit.....could be worse...could have to replace an entire AC unit.

Thanks guys,
Scott
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Old 05-23-2016, 11:35 AM   #10
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Yah I see that now on the schematic for the wiring. Might try just replacing that first...then the motor if that isn't it. Motor isn't bound up or feel any resistance so...we will see.
1. Make sure all power to rooftop unit is off (at circuit breaker)
2. At the capacitor, remove wire from terminal marked "fan"
3. Measure resistance between this wire and terminal marked "common" on capacitor.
4. If this resistance is infinite your motor run winding is open (bad), replace the motor.
5. If the resistance is some 10's to 100's of ohms, it's MOST likely a bad capacitor - change it.

It's far more common for the capacitor to fail than for the motor to fail. Good service practice calls for capacitor replacement anytime you change a motor. There's nothing to lose by trying the capacitor change first.
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Old 05-23-2016, 01:18 PM   #11
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Ok the motor reads 68 ohms so the winding isn't open.

SO which capacitor is the one to replace. The large silver cap with both the comp and fan connected to it is listed as the run capacitor on the schematic and the black solitary one off to the side is listed as start.

I mean seams the start is the one to replace but I think that is the hard start cap for the compressor..or am I wrong.
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Old 05-23-2016, 01:20 PM   #12
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Plus after fiddling with it up top it did start on it's own a few times albeit a bit slow. Oddly when i spun it I had it going backwards....dohhhh. So one would assume it is the cap.
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Old 05-23-2016, 01:29 PM   #13
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Here is a PDF I just bumped into for troubleshooting the system including the caps. This is for my AC but should be similar to other DUo Therms.
http://bryantrv.com/docs2/docs/olderac.pdf
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Old 05-24-2016, 12:46 AM   #14
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Ok the motor reads 68 ohms so the winding isn't open.

SO which capacitor is the one to replace. The large silver cap with both the comp and fan connected to it is listed as the run capacitor on the schematic and the black solitary one off to the side is listed as start.

I mean seams the start is the one to replace but I think that is the hard start cap for the compressor..or am I wrong.
There is no start capacitor for the fan. The fan has only a run capacitor. The compressor may or may not have a start capacitor (depends on model).
When you examine the metal can capacitor you will see 3 groups of terminals, with the center group labeled "C" or "Common" one of the end groups of terminals will be marked "F" or "Fan", and the group on the other end marked "H", "Herm" or rarely "Comp". This device is actually two run capacitors in a single can, with both sharing the common terminal.
The fan uses the run capacitor that is between the "Fan" and "Common" and the compressor uses the run capacitor that is between the "Herm" and "Common".
Run capacitors remain energized the entire time the motor is running. They generate a good deal of heat, and thus are in metal cans to help dissipate this heat.
A start capacitor, if present, will be a plastic-cased device wired only to the compressor. It also will have some type of relay device to switch it out of the compressor circuit once the compressor is up to speed. If this start capacitor is not switched out, it will overheat and explode.

Your best step is to carefully remove the dual run capacitor - taking special care to tag each removed connection to identify from which terminal it was attached to. Then take the capacitor to an RV parts place, an HVAC parts place, or an electrical supply house. They will interpret the markings on the capacitor (microfarad and voltage rating) and provide a replacement.

A service tech, knowing what he is doing, can replace just the fan side of the dual cap with a replacement single cap. It'd only save you a couple of dollars over replacing the entire dual cap.

Most small (fractional horsepower) AC motors have run capacitors only. The role of the run capacitor is to increase the efficiency of the motor. It provides no "starting boost". It will, however, prevent the motor from starting if it fails open. Because a run capacitor is always energized, it undergoes a lot of stress due to heat and electrical spikes. They are the single most frequent cause of these motors not starting. Many perfectly fine single-phase, fractional-horsepower AC motors are changed when only the capacitor was at fault.

This advice provided free of charge by a 20yr licensed HVACR contractor and community college HVACR instructor.
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Old 05-24-2016, 01:10 AM   #15
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The compressor works....just ran the AC and it gets cold...just had to hand spin the motor.

So no big I guess. Order the motor kit.....could be worse...could have to replace an entire AC unit.

Thanks guys,
Scott

If it is a dual capacitor or dual purpose then try removing it and taking it an AC or refrigerator repair shop. I found a near match for my home AC one Saturday while the commercial refrigeration shops and warehouses were all closed. Worked fine then did an image search on Google til I found an exact replacement on line. Had it within a week. The near match is in my share part's drawer.
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Old 05-31-2016, 01:55 PM   #16
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O.K...turned out to need a new motor. The dual cap was fine.

SO I ordered the appropriate kit off of Amazon. Comes with motor..fan blade for heat exchanger and a new squirrel cage fan and a new capacitor.

Now it is not a new dual cap....just a single 10uf cap because..the old fan uses the 5uf side of the dual cap and the new motor is 10uf so they send a single 10uf cap which you just gang off of the common on the Dual cap.

Was not fun getting the old fan out. Could not get the squirrel cage off. Had to basically bust it off. No room to work in there....the condenser sits right in the way.

Took three hours out and in but got it done and works fine. Cost was about $110.00 for the kit.

Only issue was they did not include any mounting strap for the new cap. They say to use the one from the old dual cap but...tardos forget you keep the old cap as you need it for the compressor. SO now to run to Ace hardware or Lowes to rig up a mount. Which is not bad but room in that box is tight.

Well.....it works...won't say it was fun either. Beats buying a new AC though.
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Old 05-31-2016, 02:39 PM   #17
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well now your good to go . best to do it all at once instead of piece mill .
everything you mentioned pointed to motor not capacitor
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