Older 7900 series blower problem

[waltham41]

This is a 86 model trailer with a Coleman 7900 series HVAC

I replaced the blower motor and capacitor a couple of months ago with new parts when the original motor gradually quit working (slowed down in rotation speed until it was at a crawl but like I said it did it slowly so it was not noticeable).

The new setup has worked fine up until the last day.

I recently smelled something each time the A/C would start up, and hearing a humming sound comming from inside the cover, took the front cover off of the blower area to discover the motor was very hot to the touch and just trying to turn, not turning. Best guess one revolution in a minute..

When the motor starts, if it rotates, it rotates very slowly, and the house lights dim and brighten several times while the motor tries to come up to speed. I think that over heats the motor and that is what I am smelling. The motor was barely moving the fan.

The last few times I have helped it get rotating to get started, once the motor gets up to speed it seems to runs ok until the A/C shuts off and then we start over again when it restarts.

With the power off to the unit, I can reach in and the fan is loose and spins fine by hand.

I have set the switch for the fan to run all of the time, since the problem seems to be at startup until I get this figured out.

Could the new motor or capacitor be going bad?

I have checked the wires, they are all hooked up securely and they are not hot even when the motor is very hot to the touch and will not start up properly without a initial spin to get it going.

[furnaceman]

If you wired it up correctly, which appears to be the case, Its possible that u got a bad motor, however, its more likely u have a bad capacitor. Is the cap buldging or in anyway disformed?
Check and make sure the capacitor wires are still connected securely, I have ran into a situation where another tech didn't check the spade connectors and they vibrated loose.
At this point I would replace the capacitor, if the new motor had an oil port, you did put in a few drops of 3 in 1 oil didn't you.

[waltham41]

The new motor is a sealed unit, I will look more closely at the capacitor and the hookups . Push come to shove, I will replace the capacitor and let you know what happens. Thanks!

[waltham41]

I checked the capacitor and the wires are secure. I put a screwdriver across the terminals (with the brown wires that go into the motor still attached) to discharge any current in it before I messed with it, and did not see a spark or anything. Is this normal?

[Robert]

Did you install correct motor and run capacitor ?


IF everything shut down correctly, there will not be a spark.



Thanks,
Robert

[waltham41]

The mobile home parts place said they were replacement parts so I have to take them at their word for it. It has worked fine for several months now so I have to assume something is going bad.

Is there any voltages I can check as far as the wires going to and from the capacitor to the motor?

I guess I can replace it, cheap way to trouble shoot whether thats the problem or not right?

I have the motor running full time right now, and it is running fine. The AC compressor kicks on and off as needed.

[Robert]

Is it in a/c or heat mode when it is acting up ?




Thanks,
Robert

[waltham41]

So far I have only seen the problem in AC mode.. would it be a help to diagnose if I started up the furnace and see if it does the same thing?

[Robert]

You're most likely going to need an hvac tech here. It is running fine in fan continuous mode now.

That happens to be same exact circuit that it runs in when you set to cooling auto.


When you have it set to fan continuous, does it struggle at start up as well ?



Thanks,
Robert

[waltham41]

Good news Robert,

I checked the fan on continuous and heat, same struggle to spool up to speed. I changed the capacitor, less than 5 bucks and the fan roared to life as soon as I hit the switch. Go figure.

Since the fan and capacitor are just a few months old, I guess either a power surge got the capacitor or perhaps just a faulty capacitor?

Really do appreciate the help, times are tough and I am sure grateful that I could fix it without having to spend a lot of money.

Philip

[Robert]

Glad it is taken care of and you're very welcome, happy to help.



Thanks,
Robert