Compressor Runs-Blower motor doesn't

[Blockhead]

Wondering if there was a way to troubleshoot fan relay and blower motor thermal protect to tell if either of these were the cause of my problem. Thanks

[JWWebster]

what you working on?

[Blockhead]

A Thermo-Pride Oil fired furnace- central air unit.

[JWWebster]

Well if your oil fired furnace works like a gas furnace then the system uses a relay to shift the fan speed from low for heat to high for AC.
A relay is mounted on the fan center of an old school furnace. The fan center has the transformer and everything built in. The relay is easily removed from the fan center. I have a a few pictures central unit fan relays

[JWWebster]

The blower motor thermal overload would not likely be the problem.
The relay would definately be the problem. The coil if open won't switch speeds on the motor. The coil could be working but the innards of the fan switch itself is shot. If you can hear the coil pull in then check for voltage between common which is usually white and the hi speed fan wire which is usually black. Low speed being red. The relay is always set for heat. To get the ac going full blast the relay MUST shift the gears on that fan by moving the contact from red and common to black and common on most american made units. So even if the coil on the relay were bad the furnace should fire off.

[Blockhead]

Just replaced the relay yesterday, worked well until today. During the heat of the afternoon the compressor ran, the blower motor would cycle on and off, most of the time off. Would the relay cause the blower to do that?

[JWWebster]

Naw that is the motor getting hot. HVAC motors do well when lubed with Zoomspout oil. The oil has a high resistance to disapation is non flammable and is the slickest thang since owl shit. No I do not werk fer zoomaliciosness. LOL You gotta work that motor by hand a little. By the way move the motor from side to side. If you have play in it over an 8th of an inch then sadly that old warrior has had it. Replacing the motor aint that bad. The cage shoud slide out in tact. Most have a quick plug. use some rustbuster to help you remove the blower wheel. Don't beat on the shaft, you will only spread it and make it twice as hard to get off. use a crescent wrench to wiggle the shaft loose instead of vice grips that is a no no. Do not want to burr up the shaft of the old motor. make a note of the wiring on the old motor. get the HVAC supplier in your area to help you with it or take pix and post them here. their are plenty of HVAC techs that can help ya on here. We have the finest HVAC techs around and then they have me.(they put up with me around here, I am old school, alcohol fueled, and braindead). LOL

[Blockhead]

Hey JW. Thanks for your help. There is 2 Electric motor shops and 2 HVAC supply houses within 8 miles of my house. I think Thermo-Pride has a lifetime warranty on some parts, bet that doesn't include the blower motor. Thanks again.