Diagnosing fan not starting with on Auto

[Analyte]

I have a 2000 Dynasty, and I've been having a weird AC issue when starting up.

The issue started when I heard it humming one night so I turned the thermostat off. Later I went to troubleshoot it, and it seemed to be cycling like normal. No issue at all with the compressor as it still cools beautifully.

I've found the fan works if on Low or High speed, but if it tries to start up on auto it will just hum. I swapped out both the run and start capacitors, but it's doing the same thing. The fan motor spins freely, and it's not hot when I check it. 

 

Ideas? Thanks

[timaz996]

Have you tried resetting your thermostat? With the thermostat in off push and hold the top and bottom buttons at the same time for a few seconds. You should get an F1 on the screen. I think. 

[Analyte]

22 minutes ago, timaz996 said:

Have you tried resetting your thermostat? With the thermostat in off push and hold the top and bottom buttons at the same time for a few seconds. You should get an F1 on the screen. I think. 

No I haven't tried that yet. I've give it a shot as the only thing I can think of otherwise is my fan motor is trying to pull more juice than it should?)

[Analyte]

Ok, I'm back on this again.

I didn't find an issue with either the run or start capacitors as both have been swapped out with no change. All tested ok in the end so I'm comfortable that it's not a capacitor issue.

The unit will try to spin up the fan, and then stop and hum. If you spin the fan manually it will take off and run no problem. Ever so often, when the unit is turned on the fan will spin up slowly and then take off on its own. Once running it will run forever if set to high without an issue other than it's a little noisy.

The unit cools beautifully, and I did notice some slack in the shaft so it's slightly brushing the ducting when running. That's likely where some of the noise is coming from. The fan does spin freely when off so it doesn't appear to have a bearing dragging 

I'm thinking the fan motor needs replaced since that's all that's left, but I'm looking for a test to confirm. Everything online pointed to capacitors, but that didn't work out for me.

 

Thoughts?

[jacwjames]

Do you have a load meter showing amps, you might have it you have an Intellitec EMS display.  You would have to run the generator and/or be plugged into a 30 amp circuit for it to display.  Turn your AC on and watch the amps, you should see a spike but not that much.

When I was having trouble with my front AC back in 2015 it was occasionally kicking the breaker so I started watching the amps.  At startup was spiking really high amps, +50 amps,  so I went on the roof and spun the motor, that is I tried, it was almost froze up, I could barely turn it by hand.  So I ordered a new one and replaced, I did notice the old one was letting the fan hit sheet metal.  I found that there were rubber isolation mounts for the motor that were wore out.  The new motor came with new mounts so it solved both problems.  

Fast forward to 2021 my wife took the rig to a dog show and commented the rear AC was making loud noise but would eventually settle down.  So when se got back I checked the rubber isolation mounts were wore like the previous one, the motor was a little tight but not froze up but I decided to replace while I was into it BUT I could not find a replacement motor anywhere. 

Earlier in the year I had been on a trip in +100F temps, the AC were working but struggling to keep up, 13.5K BTU units.

So I just bit the bullet and replaced both AC's then.  ~$3K but I wanted to be confident I had good AC.   Installed 15K BTU units front and back.  Now 1 AC can easily keep up in temps approaching 90F. 

 

[Bill R]

@Analyte you might want to make sure you have the correct size run capacitor.  You can check by looking at the nameplates of the fan and compressor for the capacitance rating.   If the run capacitor is under sized it can cause issues.  Also if you have a VOM with capacitance capability you can test the capacitors.  They just need to be complete disconnected when you do.  

[Analyte]

20 minutes ago, Bill R said:

@Analyte you might want to make sure you have the correct size run capacitor.  You can check by looking at the nameplates of the fan and compressor for the capacitance rating.   If the run capacitor is under sized it can cause issues.  Also if you have a VOM with capacitance capability you can test the capacitors.  They just need to be complete disconnected when you do.  

The capacitors are the correct size. I had pulled the originals to see what was needed, and then bought replacements that matched up. Both new and old capacitors checked out ok, I had a guy at work check them both when the new parts were doing the same thing 

1 hour ago, jacwjames said:

Do you have a load meter showing amps, you might have it you have an Intellitec EMS display.  You would have to run the generator and/or be plugged into a 30 amp circuit for it to display.  Turn your AC on and watch the amps, you should see a spike but not that much.

When I was having trouble with my front AC back in 2015 it was occasionally kicking the breaker so I started watching the amps.  At startup was spiking really high amps, +50 amps,  so I went on the roof and spun the motor, that is I tried, it was almost froze up, I could barely turn it by hand.  So I ordered a new one and replaced, I did notice the old one was letting the fan hit sheet metal.  I found that there were rubber isolation mounts for the motor that were wore out.  The new motor came with new mounts so it solved both problems.  

Fast forward to 2021 my wife took the rig to a dog show and commented the rear AC was making loud noise but would eventually settle down.  So when se got back I checked the rubber isolation mounts were wore like the previous one, the motor was a little tight but not froze up but I decided to replace while I was into it BUT I could not find a replacement motor anywhere. 

Earlier in the year I had been on a trip in +100F temps, the AC were working but struggling to keep up, 13.5K BTU units.

So I just bit the bullet and replaced both AC's then.  ~$3K but I wanted to be confident I had good AC.   Installed 15K BTU units front and back.  Now 1 AC can easily keep up in temps approaching 90F. 

 

I did look at amps in my early diagnosis. No big swings when running so I didn't go in that direction further. The breaker has never been kicked so that also led to me to think it was trying to pull more juice that should be needed.

[Tom Cherry]

On 6/11/2023 at 3:55 PM, Analyte said:

I have a 2000 Dynasty, and I've been having a weird AC issue when starting up.

The issue started when I heard it humming one night so I turned the thermostat off. Later I went to troubleshoot it, and it seemed to be cycling like normal. No issue at all with the compressor as it still cools beautifully.

I've found the fan works if on Low or High speed, but if it tries to start up on auto it will just hum. I swapped out both the run and start capacitors, but it's doing the same thing. The fan motor spins freely, and it's not hot when I check it. 

 

Ideas? Thanks

Reading all your posts, then there may be a problem in the Control Module.  You do NOT have the Intellitec EMS so it is NOT a load shedding issue.  The HVAC Control modules are pretty robust....but even Superman wimps out from time to time when he is exposed to Krytonite.  BAD ANALOGY.  SO...if you have the SAME tonnage or K BTU units in the front and back, then do one of two things.  Swap the motors or swap the Control Units.  

NOW, I just found something that may be helpful.  This is a trouble shooting guide dated 2002.  I had it for my Camelot...which is an 2009.  If you read it, there is a section for MOTOR.  There is a 6 pin plug for the motor.  WOW...how about that.  You should check.  The guide says there SHOULD BE CONTINUTITY between all windings and WHITE.  Never knew that.  Start from the front and work your way back to the end.  If there are more sections on the motor.  BUT, if you have the infamous 6 pin harness....then follow directions.  You MAY have a shorted out or open circuit in the winding for AUTO....whatever speed that is.  Maybe it is variable as some Air Handlers for heat pumps have variable speed motors.  In the HP mode, you want a really LOW air flow.  Kick up the RPM or the CFM and the air feels COOL...so the HP have a lower CFM.  BUT, when you want cooling, that motor will be in TURBO as the faster the air flow...the cooler it feels.

OK....just did some MORE reading.  There is a specific circuit layout for the 6 Pin connector.  That should help.

It MIGHT be interesting...if you could measure WHICH pins on the 6 pin harness from the control module have AC on Low and High.  THEN which Pins have voltage for Auto.  Do that on the one that is working.  THEN compare to the front.  I'm of the opinion you MAY have a shorted motor....and the Auto winding(s) are shot.

BUT, you never know....

Good Luck.

ccc5 Trouble Shooting.pdf

[Analyte]

1 hour ago, Tom Cherry said:

Reading all your posts, then there may be a problem in the Control Module.  You do NOT have the Intellitec EMS so it is NOT a load shedding issue.  The HVAC Control modules are pretty robust....but even Superman wimps out from time to time when he is exposed to Krytonite.  BAD ANALOGY.  SO...if you have the SAME tonnage or K BTU units in the front and back, then do one of two things.  Swap the motors or swap the Control Units.  

NOW, I just found something that may be helpful.  This is a trouble shooting guide dated 2002.  I had it for my Camelot...which is an 2009.  If you read it, there is a section for MOTOR.  There is a 6 pin plug for the motor.  WOW...how about that.  You should check.  The guide says there SHOULD BE CONTINUTITY between all windings and WHITE.  Never knew that.  Start from the front and work your way back to the end.  If there are more sections on the motor.  BUT, if you have the infamous 6 pin harness....then follow directions.  You MAY have a shorted out or open circuit in the winding for AUTO....whatever speed that is.  Maybe it is variable as some Air Handlers for heat pumps have variable speed motors.  In the HP mode, you want a really LOW air flow.  Kick up the RPM or the CFM and the air feels COOL...so the HP have a lower CFM.  BUT, when you want cooling, that motor will be in TURBO as the faster the air flow...the cooler it feels.

OK....just did some MORE reading.  There is a specific circuit layout for the 6 Pin connector.  That should help.

It MIGHT be interesting...if you could measure WHICH pins on the 6 pin harness from the control module have AC on Low and High.  THEN which Pins have voltage for Auto.  Do that on the one that is working.  THEN compare to the front.  I'm of the opinion you MAY have a shorted motor....and the Auto winding(s) are shot.

BUT, you never know....

Good Luck.

ccc5 Trouble Shooting.pdf 672.56 kB · 2 downloads

Tom,

Thanks for the guide, I really appreciate it. I'll take a look at it and see about comparing measurements between my two units.

I hadn't thought about a winding failure, but when I think about it that does sound plausible.

[Analyte]

Well, as luck would have it the fan quit working at all this weekend. I had read the guide and planned to take some readings, but I had it on so I could make my way up to the roof and it just quit.

The wife turned it off, and I was still able to spin the motor by hand. She turned it on, and the motor just hums. I tried to help it out spinning it by hand, but it doesn't help.

So armed with the AO Smith model number, I'm going to do some searching tomorrow to see what's out there to swap in.

[Analyte]

I've been looking at fan motors on and off today, and it seems AO Smith was bought/merged out by Century.

They don't have my exact motor, F42C02A61, but according to the part # it seems to point to the ORV4540 as the replacement. The specs are close except my original motor is 3.3 amps and the 4540 is only 2.5 amps plus the original is 1/4hp whereas the replacement 4540 is 1/5hp. The mounting also appears slightly different, but probably easily modified.

I'm thinking this isn't a great replacement as it's less power and amps so it will likely move less air overall even with the same 1650rpm max? I'm not finding a century with the exact spec's so I guess this 4540 is the closest replacement rather than the exact replacement.

Anyone know of other options available? Thanks!

[jacwjames]

This is what I bought in 2014 when my front fan motor failed (essentially seized up).  My AC was a Dometic 13.5K BTU

https://www.adventurerv.net/dometic-penguin-motor-kit-with-cap-bracket-p-21975.html

They do have the Dometic PN listed and if you search using that you get lots of hits. 

 

[Analyte]

2 minutes ago, jacwjames said:

This is what I bought in 2014 when my front fan motor failed (essentially seized up).  My AC was a Dometic 13.5K BTU

https://www.adventurerv.net/dometic-penguin-motor-kit-with-cap-bracket-p-21975.html

They do have the Dometic PN listed and if you search using that you get lots of hits. 

 

The Dometic part number for the AC unit itself? I was using the AO Smith number but I'll give that a shot. Thanks 

[jacwjames]

This was the parts list for my AC

1 Air Conditioner heat pump.pdf

[Tom Cherry]

16 minutes ago, jacwjames said:

This was the parts list for my AC

1 Air Conditioner heat pump.pdf 109.25 kB · 0 downloads

Amazon as well as some of the NON OEM motor vendors will often use the Dometic PN in their "Works the same as ..." description.

[jacwjames]

In 2021 I was having with issues my rear AC, it was making a noise at startup, but would settle down.  Motor wasn't seized but but wanted to make sure they were both up to par.  Wanted to replace the rear AC's motor, there were none to be found.  Others said to buy a generic one and make it work but I was skeptical. 

After thinking about it I decided to just go ahead and replace both AC's, PPL had a good sale on the Dometic 15K BTU high capacity, so I bought 2 and upgraded to the MicroAir Easy touch.  Cost was ~$3K. 

Now a similar AC is over $2K for one.   

The 15K BTU unit may be overkill but I can easily cool the coach with one AC in temps in the high 80's in full sun. 

[jacwjames]

11 hours ago, Analyte said:

The Dometic part number for the AC unit itself? I was using the AO Smith number but I'll give that a shot. Thanks 

The part that I linked also includes the mounting bushings.  The mounting bushings were wore out on the motor I pulled out which allowed the motor to squat and as a result allowed the fan to hit sheet metal making noise at start up. 

[Analyte]

1 hour ago, jacwjames said:

The part that I linked also includes the mounting bushings.  The mounting bushings were wore out on the motor I pulled out which allowed the motor to squat and as a result allowed the fan to hit sheet metal making noise at start up. 

Surprisingly, the bushings looked great on the motor. No doubt they have been swapped before.

If I was home or close to home with all my stuff an A/C replacement might be considered more heavily, but with me out working in CA I don't want to have to pay someone to do it. The campgrounds will let me get away with swapping a motor, plus I enjoy doing things myself.

Thanks for the file and the help!