Wards gas heater problem

[Grafilthy]

A customer has asked me to look into why their Wards Gas Heater 50,000 btu
isnt blowing warm air. I believe this unit was built in 1951 as the ser. # is simply 6-51 .At the back of the unit is a 3.3 inch 115 volt motor , which i removed to test for operation. after coaxing the motor with a good cleaning and a little oil in the lube tunnel it spins at all of its rated 1150 rpms. And this is on the workbench.{Benchtest.}
rather than put the motor back on the unit i decided to test voltage at the two wires feeding the motor , which i cut for motor removal.
between the two wires i get .5 volts
from the hot of the 2 wires to the frame of the unit i get 120v.
that is with the thermostat on set to 75 deg.
My question is , any time the thermostat is on shouldnt i get 120 between both wires * which would then power up the motor to blow warm air. there is some sort of control that the motor leads originate from and im suspecting its the culprit as to why no power between motor leads. Not even sure what the control is called but i will remove it to get better aquainted with it.
Any advice is appreciated and needed.

Graf. Wards Gas Heater 50,000 btu
Appliance # 150f-6210a
Ser # 6-51

[heatseeker]

If the motor is running you should get 120 to ground on both wires. The main thing to check on a motor when it is running is the amp draw. If above rated amps motor is history. Anyways sounds like a control voltage problem as opposed to a motor problem. Is the furnace igniting and if so what goes on after.

[Grafilthy]

If each leg is 120 to ground that would make it a 240v motor . Wouldnt * Im pulling out the control box this afternoon to take it in to a supply house to try and get a suitable replacement.
Ive scoured the internet and cant find a single thing about this heater . Prestons as far as I know starts around 1960 *

Well if anyone has a link where i could find schematic of this unit i would be very happy .

Thanks. Graf.

[heatseeker]

If the motor is energized you will read 120 volts to ground from both legs- if not than 120 from hot leg 0 from nuetral.

[heatseeker]

If your motor is not any good you will probably not have any voltage through it but if it is frozen you will get voltage through the motor. You had mentioned that you had .5 volts through the motor is that energized or not * If energized the windings are open if not than you should be testing with ohms have you tried reading the * The overall problem with this POS is the fact that it is obsolete, they don't make a motor for it anymore3, you might get lucky and find a good fit but good luck. Also, FYI, If you do not know how to troubleshoot a simple 120 volt motor I would definatly not be working with somebody's 50 year old gas furnace. So before you get yourself in too deep with your limited engineering degree call a company.

[Grafilthy]

As I stated in my first post... The motor tested fine , But thank you for your concern about knowledge and what I should and should not be working on. And thanks to the rest of you as well .

[heatseeker]

you said in your original post that you had to coax the motor to get it started, that would tell me that the motor is faulty assuming that by coax you mean spinning it by hand. If not disregard.

[john_rambo]

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[how]

A furnace from this age period would not just turn on the motor with a thermostatic call for heat but would do so only when a temp /limit control probe in the exchanger became hot enough. 120F to 135F in the air side of the heat exchanger was the usual adjusted temp range for normal running.
.
When the motor failed in the furnace then that furnace went from a probable operating temp of 150F right up to 200F. Those limit safety controls usually reset themselves so that very old heat exchanger was probably subjected to over heating many times before you arrived on the scene. Fixing that furnace without having the skill sets to asertain the integrity of that heat exchanger would be an invite to carbon monoxide the very friends you are trying to help.

[Chillerman]

Well, Grafilthy, it sounds like your on the right track, but Do amp the motor once you get the blade back on, but you probably do have a problem with your fan control. Doing a good job!