I have a Bryant HVAC which recently stopped working. I was trying to use it for AC and it appeared the blower motor does not turn on, but the AC condenser seems to be putting out a cold output.

Once turned on, the system seems to run for ~1 minute, the blower does NOT go on, and then it shuts itself down.

I tested the heater setting where the same story repeats; the blower never comes on.

I proceeded to test the control board forward to the motor and so far I see that between HEAT or COOL and common I have 120V with the system on (isn't this supposed to be more than 120V?).

The resistance between the different leads going into the motor was next. I have HEAT, COOL, Spare-1, Spare-2 and BLW (BLW = common?). Resistances are around 1.2 ohm, 1.7 ohm, 2.2 ohm and 2.4 ohm - does this sound reasonable?

I do not have a multimeter with uF measurement to look at the capacitor status so that is the only one open point.

Does this sound like a good debug strategy? Anything else I should check or what to look for?

Thank you all!

 

Welcome to the forums.

That is correct. This allows for two different blower speeds.
Usually high for cooling and one step slower for heating.
Bryant gas furnace...... correct ?

You have a four speed blower motor. One common wire and four speed wires.
When you check for 120v..... did you check from hot or cold to the same exact neutral tab where the motor is connected ?

You have voltage and the windings are good.
If there is a question about capacitor quality.... replace it. It'll be 5-8 mfd.
Usually if the cap is bad..... the motor will sit there and hum without starting.

 

Thank you! This is a Bryant furnace

Yes, I thought about the capacitor, it's a 10uF and I don't have a voltmeter with capacitor testing ability so I just ordered another one just in case to replace.

The whole system is about 15 years old and I don't think the motor was ever changed (based on the accumulated dirt which I cleaned off), not sure about the capacitor.

Thanks again!

 

Like I mentioned.... if the cap was bad..... usually the motor just hums. Pretty loudly.
The motor would also get quite warm. You could power it up for 5-10 minutes and then check the motor for heat.

 

I have removed the whole assembly and won't be able to test it for a few days.

If the motor resistance tests are good and the cap is good (or bad but I will change it), and the mainboard is supplying the 120V, could there be anything else that prevents the blower to run?

Thanks!

 

Hello All,

Just to bring this to a partial closure - it did turn out to be the capacitor, the old one was bad showing 0 uF. Replacing it and the blower runs as good as new.

I have another issue with the AC outside condenser running for a long time after fixing the blower, it initially worked and cooled off great but after a few hours it turned off and the outside motor does not spin up anymore. When the thermostat kicks in or the system is started there is a click and the compressor kicks in for maybe 30 seconds after which it shuts off. The fan never runs (is that expected right at the start)?

 

You could have the same problem with a capacitor in the outside condenser.
You may have two out there..... one for the compressor and one for the fan or a dual type.

Usually if the fan starts ok when cool but not after it has run for several hours it's a sign of worn bearings. Replacing the cap is the least expensive place to start.

 

Thank you, I just pried the cap out of there and it reads 0 as well. Very strange that the same failures would be on two systems within a short time of each other.

I'll replace this and see if it fixes the issue. Just to confirm, the fan should kick on as soon as the system starts, correct (i.e. it would not be a delayed start/etc.)?


Thanks!

 

Yes..... that is correct.