Payne Furnace Blower Motor Problem

[markshew]

I am a new member of this forum and am hoping that some of you cleaver people out there can help me with my problem.

I have a 1990 vintage Payne series A forced air furnace with two problems both associated with the blower motor.

The first is when the blower motor is first switched on. The motor starts to turn but does not quite reach speed and goes off for a few seconds. The motor then switches back on and the second time it spins up to speed just fine.

I took the blower motor out, cleaned and oiled the bronze bearings and also replaced the filter and this seems to have improved things. I was wondering if replacing the run capacitor would be worth a try?

The second problem is at the other end of the furnace cycle when the blower turns off. The motor stops turning for a few seconds, comes back on for 2-3 seconds, and repeats this cycle 2-3 times.

After looking at the (partial) diagram on the inside of the furnace and searching this forum, I wondered if the plenum T/stat was the likely cause of this problem? (The sensor is a STEMCO 430-1457 HH12ZA174c).

Any suggestions welcome.

Thanks!

[HayZee518]

take the motor apart again and clean off the centrifugal switch contacts. use a piece of 400 grit sandpaper NOT emery cloth. make sure the flyball weights are free to move outward. look at the nylon rubbing block on the flyball make sure it isn't grooved. what this does is disconnect the start capacitor when the motor is up to running speed. when you re-assemble the motor if there are any fiber spacers, make sure you got the proper number on either or both sides. these help keep the rotor centered in the magnetic field. a little bit of slide slop is ok. the plenum stat is a hi limit and run limit. if the proportional band is too close then the switch will be telling the motor to operate.

[markshew]

First of all, thank you so much for the prompt reply!

I had no idea that there was a centrifugal switch within the motor itself so I will have another go at that as you suggested.

I should have also mentioned that I added an in-line booster fan to help circulate the air to the upper level of the house. I took the power for the additional fan straight off the control PCB using "piggy back" spade connectors where the main blower motor gets it's feed. The start problem seems to be less prevelent if I switch off the booster fan (I added a rheostat to control the booster fan speed). I wondered if this was part of the problem by wearing out the relay contacts prematurely due to the additional load?

Regarding the plenum stat. There is no adjustment that I can see on the unit so do you suggest replacing it?

Also, when I looked at it again today, I found that there are actually what appear to be another stat / sensor in series with it, with the 2nd one being a TO3 metal can configuration mounted on a part of the furnace where air is drawn in and mixed with the combusted gas. Both the plenum T/Stat and this second sensor appear to be "normally closed" when measured with an Ohm meter with the furnace off.

[HayZee518]

a rheostat is fine where you control the speed of a dc motor but I wouldn't suggest it in an ac motor. for that a tapped autotransformer works best but these tend to be pricey. I got one for my bench testing that goes from zero to 130 volts ac. cost about $50. the can type "stat" is a klixon overload that uses a bi-metal switch. when it heats up it opens, when it cools down it closes.

[markshew]

Again, thanks for the prompt reply!

After your advise about not using a rheostat to control the booster fan speed, I went to remove it and discovered that it is actually a fan speed controller made by Leviton {6616-1XL). After checking the spec sheet it seems to be OK for the application but I would appreciate your input.

BTW, do you expect that the cleaning of the centrifugal contacts will help with the starting or the stopping problem?

What I thought was the plenum stat looks to be an overtemperature sensor in the heat exchanger as the gas supply is cut off when it is disconnected. I will have to look elsewhere for the plenum stat.

[markshew]

Well, I took the motor apart as suggested and low and behold, no centrifugal switch contacts at all! There was nothing inside the motor apart from the stator and windings so now I at a loss as to what to do next. The only thing that I can think of doing is to change out the run capacitor.

Failing that, I may have to admit defeat and call in the repair man.

Any other suggestions anyone?

[jnaas2]

The capicator you are talking about if its a start capicator it will be light if you remove it, if its a run capicator it will be filled with oil and be heavy for its size, it shoud say somewhere what it is. The one thing that will cause a fan to turn off and on is the fan control its a sguare looking box that also is the high temperature limit and if you take the cover off it will have a circular dial with temperature readings on it. If your furnance is circuit board controled it may be going out. If you can send a wiring diagram it will be easier to answer your question

[hvacwiz]

I would suggest instead of spending all your time screwing around with it, to shell out 80-100 bucks for a new motor and be done with it.

[markshew]

Jnaas2

Thanks for the suggestion.

I have absolutely no problem buying a new motor but I would like to understand why it is that you think that the symptoms I describe are due to a bad motor?

I am an engineer and really dislike just changing parts out and not understanding the problem.

Thanks,

[jnaas2]

Markshew
Im like you I have a lot of fun trying to figure out why something doesnt work, and PATTING Myself on the back when I get it right the first time. Im not a engineer but I hold a Master electrician license, Master plumbing license and a Commercial and Residential contractors licenses. Lets us know what you find out

[markshew]

Thanks for the words of encouragement!

You said it would be helpful if I could provide a circuit diagram for the furnace, well, unfortunaltely, it is stuck to the inside cover and not in very good shape but I have taken some photos of it and would appreciate you taking a look if you are interested.

The last time I tried to attach a file the system would not let me so, if this does not work, maybe I can send them to you direct?

Thanks,

[markshew]

another shot of the diagram.

[markshew]

Problem Solved!!!!!!!!!!

For anyone out there who is interested, I managed to solve my problem without having to resort to calling in a repair man!

After studying the circuit diagram and doing some searching on the internet, I decide to try replacing the blower motor control board.

I managed to source an exact replacement board from Furnace Parts, Hvac Parts, Airconditioning parts for under $80 including tax and shipping.

Installation was a fairly straighforward task involving labelling and removing all of the connections and from the old board and connecting up to the new board (something that I learned that would have helped me out is to take a couple of close up digital pictures of the connections just to have as a reference).

After making all of the connections, the blower motor worked perfectly!

I hope this is helpful to someone out there.