Air Conditioning - Blower motor is... blown

I recently had a guy come out to look at my HVAC unit. He said that my blower motor might be going bad and my contactor and my condenser fan motor were caput then generously offered to fix it for me for 1500 dollars :thumbdn: .

I found a granger and purchased both parts for $91.00 and installed them myself.

I slip in the breaker and the whole thing come on purring like a kitten. At this point I go into my house and feel cool air coming out of the vents.

Here comes the problem.

Suddenly I hear a muffled bang and smell an electrical fire. I go to my AC and the thing is still running but the blower motor is now not moving.

I purchase a replacement thinking that its the motor just going out and put in in for $70.00. I slip in the breaker and the whole thing comes on. Im sitting in front of the open panel that the blower motor is in and i hear a muffled explosion and see fire inside the blower motor!:madhell:

I'm assuming that there is something wrong with the way I wired it. I'm almost positive that I put the wires on exactly how they were on the original parts. Can anyone help?

did you use new matching capacitors with the new motors? I take it voltages, rpms and horsepowers were matched?...not enough info to really judge from here. Might be time to dig out a volt meter and verify what's going on.

I did get a new matching capacitor and I made sure that all of the specifications on the motor were the same.

Is it possible that the contactor has something to do with it? or that two different speeds are trying to go on at the same time and shorting the motor?

Im not very well versed in electrical unfortunatly. What would the volt meter show me and how would I apply it?

It sounds to me like the voltage is wrong on your motor. Need details, furnace or air handler, wire choices etc.

Old Blower-
Volt 208-230
R.P.M. 1075/4SPD
HZ 60
AMP 4.4
PH1
HP 1/2

New Blower-
Volt 208-230
R.P.M. 1075/3SPD
HZ 60
Amps 3.8-3.7
HP 1/2

They seem to be comparable to me and I wasn't using all the speeds on the old motor so the speed difference wasn't an issue.

I used the original wiring and connected it to the blower motor with wire nuts. Its a unit on the roof and its all in the one unit. Heating and cooling. Its a Heil unit.

Could it be the way that I connected the capacitor? maybe the wires on the wrong sides? I don't know a lot about HVAC so forgive me if I sound ignorant.

The condenser fan motor is working great though...

You should be using one speed for now just to get something working so use the black and white wires for power and two brown wires for the capacitor if you had an additional wire on your capacitor use that for one of your line voltage wires (black or white).
http://www.bardhvac.com/digcat/techdoc_cd/pdf-file/4096-141.pdf
Here is a sample diagram look at the evaporator section (top left) for a typical four wire setup.
When you get it running then you can pick another speed for heating then follow the other wire back to the heat terminal on your control board.

I'm worried that if i connect it up again that I will blow another motor!

I took out my voltmeter and the cold wire and the com line both showed 121 but the hot wire didnt show any reading at all. Does that mean anything to you guys? by hot and cold i mean that they plug into spots that say hot or cold on the board.

the motor is a 208-230 does that mean that I am not getting enough volts?

Would plugging in only one speed (cold) be OK and not blow my motor?

I have the two brown wires a black wire that is my high speed a purple wire that is my mid speed and a red wire that is my slow speed.

Could something I did with my conductor when I installed it be doing this? Is it even possible to put them in upside down?

I dont mean conductor I mean Contactor...

Thank you both for looking at this problem for me.

I appreciate it!

I tested the voltage on the board for the cold hot and com lines. both Hot and Com read 121 volts but the cold was showing 4v max. Is my board bad?

Also I plugged in a new motor with only cold wired to a speed = nothing happens.

I wired up hot to a speed and my motor turned on but was making bad noises and started to smell. The motor was being burnt out! I pulled the breaker before it could go to far.

What does that all add up to for you guys?

On a 208 to 230 circuit there are two 'hot' legs. L1 & L2, which will have 208v - 230v potential between them, and 120v between each of them to Ground (usually a green insulated wire) and the cabinet/frame.
L2 could go directly to the common on the motor or through the board, while L1 is switched either through a stand-alone relay or relay(s) on the board. Cooling would be the high speed, heating either low or medium depending on the ductwork's static pressures.
It's possible to get bad motors right from the distributor, especially the cheap ones, as in=> made in the far east.

Study the schematic...

The contactor was the problem. I think that one of the poles was bad and I wasn't getting enough voltage to the motor. The motor amped itself up and burned out because it was trying too hard.

I replaced the contactor and the problem went away.

Thank you all for the help.

Low voltage to the motor caused by dirty/burnt contacts will cause an increase in amperage drawn by the motor, with a corresponding increase in heat - melting and burning the varnish insulation on the windings, and possibly melting any soldered joints. Hope you found it before burning another motor.:madhell:

I did catch it before unrepairable damage happened. The contactor was brand new from the box.

I think I heard from an electrician friend that they sometimes just come bad from the factory. Apparently he has had problems with this sort of thing as well.

What you described is exactly what happened to my first motor...

After that I couldn't get a motor with the right shaft diameter and HP because Heil had this one made to specifications apparently to discourage DIY-ers. I ended up getting a correct hp motor and went to 10 different HVAC shops looking for an adaptor for the shaft. Its purring like a kitten now and I haven't had problems with it... yet. Beer 4U2