I have a Bryant/Carrier 394GAD furnace. Original with the house built in 1991. It's been very reliable until recently. I plan to replace it in the spring once my daughter is out of college, just trying to get through one more winter without spending big $$.

Last week during the heat wave, the AC didn't blow cold and the refrigerant line was frozen. I believe the blower motor fan in the furnace was still blowing at that time, but I could be wrong. I didn't do anything about it since it was probably going to be the last hot day of the year.

I went to fire up the furnace for the first time yesterday, and the burners light, but the fan will not start. There is a distinct humming sound coming from inside the furnace. When I kill power to the furnace, the buzzing sound stops.

My first inclination was a bad capacitor on the air handler/blower motor fan. I peeked inside the box and I saw no capacitor mounted in the usual location. I removed the squirrel cage (with plans to clean it thoroughly) thinking it was located inside, but no... I do not see a capacitor.

1) Is is possible the motor has a capacitor built in? I plan to unmount the blower motor to get the motor model number. I would think that would give me some direction.

2) Would the blower motor not starting have been a cause of the AC not starting up? My experience is that when the air doesn't blow across the evaporator coil, that would cause the frozen lines (along with a lost of other problems, like low refrigerant, etc).

I noticed that when I spin the fan in the squirrel cage, it turns for maybe 1/2 to 3/4 turn. I thought it should spin more freely... so I'm thinking it's a bad blower motor.

Any advice is greatly appreciated.

 

I would expect the blower to turn more then 1/2 or 3/4 of a turn. It would be unusual for the motor not to have a capacitor but sometimes they are remotely mounted. If there are any brown wires going to the motor, follow it/them & you will probably find the cap.

 

It sounds like your blower motor has bad bearings.

Some old units shipped with a type of motor that doesn't use a capacitor.

Edit: I just looked up the model - yours indeed uses a shaded pole type motor. No capacitor.

if you end up putting a new blower motor, you can convert to a common type that uses a capacitor. the new cap just gets attached to the blower assembly with strapping.

You'll have to match the motor frame size, shaft thickness and hp. You can't match by amps motors with capacitors draw less current.

 

Thanks for the feedback. On the turning... I would think it would spin freely like a bicycle wheel, at least 4 or 5 turns. So the motor may actually be the issue.

No brown wires. Still perplexed on the cap...

I pulled the motor from the bracket. After pulling the motor, there is some noise inside when spinning it.

The motor is AO Smith 319p899 115v 1/6HP 4speed 1050 RPM

I'm not having much luck finding OEM online. Any suggestions on where to find a replacement is greatly appreciated.

 

It's almost impossible to find a replacement motor based on an old model number.
You need to use the full furnace model number and replacement motors can be found.

On a quick lookup...... I'm seeing $200 for a blower motor.

 

Read my reply again - There's no capacitor because the existing motor is shaded pole.

I wouldn't use an oem motor especially on something that will be replaced soon.

Get the cheapest universal blower motor you can find with the correct rpm, hp, frame size, shaft thickness.

Most universals can have the rotation reversed if need be.

Some of them are multi-hp and you to use the right capacitor and speed tap to match what you have now.

If you post all the information on the motor's rating plate and a picture of the mounting, we can help you find another one.

The full model number of the furnace may be helpful to see what a site like repairclinic recommends. the specs of the recommended motor can be used to find a replacement if the motor doesn't have the information on it.

---
Keep in mind, a lot of old motors have oiling ports.

If your does, it's absolutely worth oiling -> if you can free the bearings it may last until spring.

 

Searching with my exact furnace model number yields this motor:

Fasco D158 -- $107 I can live with that.
https://www.repairclinic.com/PartDet...r/D158/2332904

SPECS D158:
Blower Motor Type:
Shaded Pole; HP: 1/5 - 1/6 - 1/7; Volts: 115; RPM: 1050; Speeds: 3; Amps: 6.7-5.3-4.7; Enclosure: Open Vent.; Rotation: Clockwise; Bearings: Sleeve; Shaft: 1/2 X 4 1/8"; "A" Dimension (inches): 3 7/8"

Here's a photo of the old motor. Where would the oil ports be? There's no play in the shaft, just a little stiff, so I'm up for oiling if I can get by with that.

 

Thanks for confirming the shaded pole motor thing.

I found a video that shows how to oil a motor with no ports.
https://youtu.be/gHVuTApqBDY

 

usually the oiling ports are near the ends of the motor - little plastic pips you remove and drip a little oil in.

Motors without ports use a grease instead of oil and aren't designed to have anything added.

If your motor has no ports, replace it.

---------
FR is frame size - it's 42Y.

I see a molex connector on that motor - for a new generic one you'll have to cut it off and splice on to new motor wiring.

If you can actually find an oem that has that connector things will be easier. $100 isn't too bad. usually oem motors are a lot more.

edit: doesn't look like it has that connector.

It says type U51 don't know if that's a match for what you have.

If you order from repair clinic, get confirmation from them in writing that the motor you're ordering is correct for your unit.

Normally I would advise against putting another shaded pole motor in a furnace since they're really energy inefficient. But when you're going to change the entire furnace soon, it doesn't matter.

 

I opened up the old motor and there was a felt-like material just inside the top of the motor, dried and crumbling. Not salvageable.

I just did another search for AO Smith 319P892 (I thought the last character was a NINE) and finding a lot more matches for new motors. Apparently AO Smith is replaced by Century. Feeling better about finding an exact match now. I'm not going to switch to another motor at this late stage of the game. Again, just trying to get through the winter.

 

You'll be fine with any motor with the same frame and other specs.

but yah if it's a direct approved replacement there's a lower chance of having issues due to mistakes matching.

 

As it turns out, there is an oiling port at the top of the motor. I pulled the plate and there was some dried out felt-like material that apparently used to contain oil. It was dry and crumbly. Even if I tried to add oil I don't think it would have helped. That material looks like it wicks the oil down into the shaft.

Without that plate in place, there is a little more play in the shaft.

I know it's a long shot, but how hard would it be to replace that wicking material, oil the motor, and plug n play? I'm guessing it'll be hard to find the exact part, but what about getting a generic version and cutting it to fit? Trying to go ultra-cheap if I can.

Looks like the weather in Ohio is going to cooperate for another week or two before we're going to need the furnace.

 

I've never done that - you may not be able to find the right material and it could fail after the repair.

Pulling the blower again is a pain and so is having no heat mid winter while you wait for the part to be delivered.

I would spend the $100 to $200 and change the motor now.

 

Thanks for the advice user 10. I'm waiting to hear back from the supplier to be sure I'm ordering the right motor.

For future reference, I think I found a supplier for the wicking material, a company called McMaster Carr.
https://www.mcmaster.com/catalog/125/3664

The material is pretty cheap. I may just order some just to satisfy my curiosity.

 

One Final Question

I got the new motor installed in the squirrel cage and getting ready to wire this bad boy up. The old motor was a 4-speed, replacement is a 3-speed. I'm assuming the speed is chosen by which wire is connected to the furnace/control board?

OLD motor wiring had a molex on the end, with the following connections. Yellow and Red wires from the old motor were wired into the Molex, but only the White, Black and Blue wires actually connected to wires coming from the furnace/control board.


OLD MOTOR ----------FURNACE/CONTROL BOARD
WHITE--------------->WHITE
BLACK(HI)----------->BLACK
YEL (MH)
BLUE(ML)------------>RED
RED (LO)

New motor has 4 wires, White, Black, Blue, Red, and motor label has the following markings:

NEW MOTOR
WHITE
BLK (HI)
BLUE (MED)
RED (LO)

I'm assuming I'll connect WHITE > WHITE, BLACK > BLACK and BLUE > RED to match the old motor?

Also, is it kosher to simply strip the wires and use the proper size wire nuts to connect the Molex to the new motor... assuming I ensure any excess is tied down to prevent it getting into the motor.

Where I'm confused - I've been reading you should never connect the line voltage to two speed leads. I'm not sure which speed is actually used by my furnace, since both the BLACK (HI) and the BLUE (MED) were orig connected to the molex.


I've included images of the old motor/molex connect and new motor.

Once again, any assistance is greatly appreciated!

 

Only one speed is energized at once. heating and cooling use different speeds in most cases.

on the left side, red is heat, black is cooling.

Connect all the available speeds to the molex connector.

C = white to white, neutral/common
1 = black on old molex to motor's black, high
2 = yellow from molex to motor's blue, medium
3 = blue from molex to motor's red, low.
4 = cap the red lead off the molex off. Don't use 4 on the speed selection side.


Medium and low will be a little different, going from 4 speed to 3 speed.

The medium low on the old motor is likely between the new motor's low and medium.



3 is low on the new motor instead of medium low. Leave red/heat on position 3 to start with.

You'll have to determine whether to use low or medium.

After the motor is installed, measure the temperature rise:

1. Run the furnace for a good 15 minutes

2. measure the temperature difference between the supply and return with a digital stem thermometer you can insert into the duct. digital cooking or lab type thermometer.

Make sure the thermometer on the supply isn't too close to the furnace as it can be thrown off by radiant heat.

It should be 1.5 to 2 feet away from the furnace in the duct.

You can drill into the supply trunk line if required, cover tiny hole with foil tape.

Check the temperature rise range on the rating plate.

If the rise is near or above the upper end of range, move the red wire on the speed selection side from position 3 to position 2 so it runs on medium.

Retest and post back if it's still outside the range.

Failure to set the fan speed correctly can cause the furnace to overheat and cycle the burners on and off during a heating cycle. damage, high fuel bills, and low heat output can result.

Yes - that's what you have to do to preserve the connector.

You can use marettes (wire nuts) or crimp connectors. Crimp connectors make for a cleaner job and they're more reliable, but honestly it doesn't matter if you're going to replace the furnace soon.

 

Thanks for the detailed response, user 10. You're a life saver!

In the schematic on the furnace, it says a 3- or 4-speed motor may be installed, and shows the same connection that you suggested.

I just noticed this looking back through my photos shot when I was disassembling. I knew that would come in handy.

 

i edited as you posted so double check.

(extra characters to post)

 

Just finished installing the motor. Decided to use crimp connectors based on your advice. I can’t believe how easy it was to reassemble.

Anyway, I ran the furnace for 15 minutes, then tested the return air (74 degrees) and found a random sheet metal screw about 2 ft above the air handler (101 degrees). Sounds luke it’s within proper range.

i also tested the AC. When we had that heat wave a couple weeks ago, the lineset was frosting up and wasn’t blowing any air. It is also working again. I let it run for about 1/2 hour and no frozen line! 2 for 2!

Thanks again for all your help User10. Greatly appreciated.

 

A 27 degree rise is abnormal;y low for a furnace especially an old one with a 1/6hp blower motor.

50F is more typical.

It's only in range if you have the 25 000 btu version.

The 50k with this motor is rated 35 to 65F, the 75k -> 55-85F.

The thermometer may have been in a poor location (the air can be cooler near the back and there can be hot/cold spots), if not the furnace is underfired.

There's no way your blower can deliver enough airflow for a 27f rise at the rated btu output unless you have the 25k which is way too small for most houses.

It may be worth testing the supply in different locations and you get similar readings, clocking the gas meter: https://hvactechhangout.com/home/sys...k-a-gas-meter/

*Don't use the smallest dial when clocking, it's not accurate.

 

the rated rise is 15 to 45 for the 25k version.

 

It's a 50,000 BTU furnace, temp rise is 35-65 or 40-70 according to the label.

I'll test again. Probably rookie mistake.

Label attached.

 

Clock the meter if it's still too low after rechecking in another spot.

You may need to have the gas pressure checked. It takes a manometer to do it, i've never had to and usually it's best left to a tech - done wrong can leak gas and cause an explosion.

But if you're sure you're replacing the furnace next spring, it may not be worth paying someone.

Does the house take a long time to warm up?

 

I don't know if it takes a long time to warm up the house. Honestly, it hasn't been cold enough to really test the furnace. It's been in the 50's-60's all week.

I haven't had a chance to re-test. I may just bite the bullet and pay an HVAC to do a pre-season check out. I can get it done for about $69 locally. (I think replacing the motor would have been a $400+ job, so I wanted to clean it up and replace the motor before hiring someone)

 

Be careful with the low priced preseason checkout “deals”. Many companies use them as a way to get their foot in the door to sell parts or a new unit.
This is especially true for companies that pay their techs on a commission based salary for how much they sell.

 

do the preliminary checks yourself because if it was just a bad reading*, no reason to call a tech out only to replace the furnace in a few months.

i don't think a decent guy will charge under $100 for maintenance.

*you used a accurate thermometer, right?

they can condemn the furnace for liability because if it has closed hairline cracks that don't leak*, is technically defective, forcing you to replace before winter rather than when you can afford it. now, i don't advocate continuing to run it knowing the heat exchanger is technically defective.

*open holes and cracks do pose a more immediate hazard.