Replacement AC fan motor very weak.

[Lazarus_Alessan]

Short version: I just replaced a failed AC fan motor. Now the fan actually works BUT it runs at around 20% of the previous speed and blows air very weekly. Also, when I set the fan to auto instead of low or hi, it doesn't blow at all. Help!

Background: I've got a Dometic 13.5K BTU ducted AC in my 2014 Coachmen Apex. A while ago the fan started having a very hard time turning on (click and hum but no turning even if I tried to spin it by hand) but after trying for a couple hours if get lucky and it would start. Once it started, it would run indefinitely. I replaced the capacitor and that didn't really help. Yesterday, I got it running after a struggle and it ran for a few hours until it started squealing louder and louder until the fan geadually slowed to a stop. I got a replacement for my model (457915.711CO) from an RV service place, same size, wire colors, wire lengths and connectors so I felt confident it was the right part. I installed it and now I've got the problem I mentioned above. Could it be a bad ground? Did I swap a wire? Anything? O was only 95% sure that I put the condenser fan back on the right way but that doesn't seem like it should me such a drastic difference in the speed the motor will turn. Any help is appreciated.

[Lazarus_Alessan]

The wires from the new and the old motors are identical.

With the current motor, low blows slower than high so I don't think they're swapped but they are both very slow. Also, "low" on the old motor was about twice as fast as "high" on the new one.

The motor had mounts welded onto it so it could only go in one way. Also the shafts were different lengths and wouldn't have put the fans in the right places if I somehow managed to still put it in backwards.

You'll have to forgive the dumb question... but the condenser fan should be pulling outside air through the fins into the AC housing right? or should it be pushing air from inside the AC housing through the fins and outside the AC housing?

[sayoung]

With it off, look at the condenser blade, it will give you a clue to rotation. .
You did get the right shaft to the right fan, ? Are these cradle mounts, I haven't worked on rv AC in at least 15 years so my memory is fuzzy.
FYI, motor rotation determined on the lead end.

[wa8yxm]

Many of those motors have multiple "hot" wires.
Low
Med
High

[Lazarus_Alessan]

Thanks for the quick replies. To answer the questions.
- The wall thermostat is a digital Dometic 3 button (+, -, mode/on/off).
- Both the old and the new motors had identical wiring. The exact same number, colors and connector type for each wire (the brown and white that go to the capacitor are a little shorter and have slide on connectors). I'm sure I connected the wiring the same way. I took pictures and was meticulous.
- I mentioned there's a very small chance I put the condenser fan on backwards but I'm completely certain the squirrel cage fan that actually circulates the air for the camper is on the correct way (it stayed inside the narrow housing and I just slid the old shaft out and the new one in.)
- the old motor almost never started but after it started it would run strong for a while then start squeeling louder and louder until it gradually slowed to a stop and would just hum.
-the new motor starts right up every time in hi, low AND auto (I was mistaken in my original post, auto mode works) but it runs much slower and it doesnt put out anywhere near as much air. It's a huge difference. It probably blowing 1/5 as hard or possibly less. The fan is much quieter too and I can see the condenser fan spinning slowly so I think it's spinning slower and not just spinning the wrong way.

How unlikely is it that this thing was already bad? It definitely looked new.

As for DIYing it. We're actually camping this weekend as I write this so taking it to a service center for it to sit for three weeks wasn't an option. As of now, it's almost keeping it livable but if it was working correctly it'll make my little camper an icebox in about an hour.

Thanks again,
-Dave

[dougrainer]

Need to know the model control system(type wall tstat) of your Dometic. Did you use all the wires on the new motor? Some Motors have extra wires that are not utilized and are supposed to be capped off. Are you POSITIVE you connected the wires to the correct terminals at the capacitors and control board? When a fan motor acts as you state, it is usually a bad motor. From your story, do BOTH the old and new motor act the same way? I cannot tell for sure from your post. Doug

[sayoung]

I my life before retirement , several times have found diy'ers sometimes put the fan blade on reversed. I think if you had wired it wrong the factory charge of smoke would have already escaped :E
Also, if you swapped the Run & Start leads to cap, the motor runs reversed. Something else to check when low airflow .
I had a red rubber stamp I stamped invoices that said, NO WARRANTY if not installed by Geezer AC, when diy guys would want to buy parts, I explained my warranty of ZIP on electrical parts but many hundreds still wanted them and yes sir , many paid us to come put a new motor on. I was a service business not a parts house.

[Artum_Snowbird]

An excellent thing to do is to run a new cable from a good power source to where the A/C connections actually are on the roof. If your A/C runs normally at that point, you have proven it to be the electrical supply. Now you try running only the original positive, and the new cable negative. If that runs normally, then you know you have a weak negative return wire somewhere. If not, then try the new positive and the original negative. It that runs normally, then you know you have a weak positive feed.

Knowing that you have a good source of power and a decent return is very often the solution when things seem to run poorly. Eventually, loose connections fail completely. Often then, expensive parts are replaced, and in doing so connections are tightened and lo and behold, it works.

[Lwiddis]

Trying to fix/replacing parts on five year old RV A/Cs is problematic. Five years old with heavy service, I’d replace.