Furnace Fan AC help!

[tonydanzah]

So I went to turn on my AC tonight and knew right away something was wrong. I got a little air blowing from the vents for a min and then nothing. So I walked outside to make sure the fan and pump were running at the condenser. Both were on, so i walked into the basement.

I found the txv frosted up and the blower fan didn't sound like it was on. I pulled the cover just to see it come to a stop. There is a on off switch wired on the side on the furnace. I turned the furnace off and waited a few minutes. I flipped the switch back on and watched the blower fan come on full speed and within 2 minutes it got slower until stopping completely.

Is this the sign of a failing blower? Can I safely jumper out the control board and try to run the fan on the medium setting to see if its the board?

Any help would be appreciated.

 

[tonydanzah]

hmmmm.......

 

[fourfeathers]

Can you run the fan full-time @ the thermostat settings? That would be easiest.

 

[tonydanzah]

You mean by putting it to the "on" setting? It turns on high then slowly comes to a stop. I have an old school mercury thermostat.

 

[tonydanzah]

after searching the internet I found a place recommended in downers grove that will test your blower and has a large stock of motors.

 

[Dave in VA]

After the motor stops can you spin the blower wheel by hand? It should spin freely. If not, then it's probably time for a new motor.

You mentioned Downers Grove--We lived on Lemont Rd in the late 50's. The state took 1/2 of our front yard for the frontage road for the I-55 interchange. It looks alot different on Google Earth then when we lived there. Our old house is still there, but everything past it is entirely different.

 

[danski0224]

You have to check the amp draw.

 

[oltruckag]

Is the blower motor hot to the touch after it runs for a min or two? Get a clamp-on amp meter and check the draw compared to the rating on the motor - I suspect you'll find the current draw is high.

It is possible the cap is bad (weak) but usually when they fail the motor won't run at all. After the motor stops on its own, give it a spin and see if it runs a bit longer. Could just be a $15 problem, not a $100 problem.

 

[tonydanzah]

the housing to the motor is very hot. I have an amp clamp and can throw it on. What is the specs and can I hurt the motor if i bypass the capacitor?

 

[Dave in VA]

It won't run without the cap. There should be a tag on the motor or the furnace with the motor amp draw. If it's hot after just a few minutes, I suspect the motor bearings are shot.

 

[danski0224]

the housing to the motor is very hot. I have an amp clamp and can throw it on. What is the specs and can I hurt the motor if i bypass the capacitor?

It's done.

Motor will not start w/o capacitor.

Motor specs are printed on a sticker that is usually covered by the motor mount bracket. Probably should be less than 10A- just a guess though.

You need a capcitior checker to test the cap.

 

[tonydanzah]

battery was dead in my amp clamp, but i did bypass the cap and the motor did the same thing. I think I have a meter with a cap setting somewhere

 

[bazar01]

battery was dead in my amp clamp, but i did bypass the cap and the motor did the same thing. I think I have a meter with a cap setting somewhere

You seem comfortable with a meter so do the following.
Turn off the disconnect. Open the electrical cabinet access door. Look at the top of capacitor mounted on the blower housing, if it is bulging at the top, it is toast, you need a new start capacitor. Usually a 5mF capacitor. If the capacitor top is not bulging, you need a capacitance tester or get an analog meter set to resistance and watch the needle. If it pegs then drops, reverse the probes, if it pegs then drops, the capacitor is good. Then the motor is shot, Do a resistance test on the motor leads, common to start terminal and common to run terminals then report your ohm readings. Also do a ground test on the run and start terminals to ground and report back.
Good luck!

 

[tonydanzah]

ok I found out my fluke 289 does have a cap testor setting along with the diode testor. There is no change on the meter when i touch the leads or switch directions. I also have a simpson 260 that I bought to check a piece of forklift potentiometer. Not to familiar with it. But set on 1ohm, 100ohm or 10k ohm the needles do not move in either direction.

 

[bazar01]

ok I found out my fluke 289 does have a cap testor setting along with the diode testor. There is no change on the meter when i touch the leads or switch directions. I also have a simpson 260 that I bought to check a piece of forklift potentiometer. Not to familiar with it. But set on 1ohm, 100ohm or 10k ohm the needles do not move in either direction.

Not familiar with Simpson 260, is it an analog meter? If it is, the test should work.
I forgot to mention, did you pull the wires off the cap when you tested for resistance? If not, pull the wire leads off the cap and retest.

 

[tonydanzah]

Not familiar with Simpson 260, is it an analog meter? If it is, the test should work.
I forgot to mention, did you pull the wires off the cap when you tested for resistance? If not, pull the wire leads off the cap and retest.

simpson 260 is analog. I pulled the cap for the furnace to bring upstairs to test it. The meter works, as the needles moves is i touch the probes together.
http://www.drillspot.com/products/118847/Simpson_260-8_Analog_Multimeter?s=1

same meter but i bought mine dirt cheap on ebay

but just like on the fluke 289 cap testor i get no change.

 

[bazar01]

simpson 260 is analog. I pulled the cap for the furnace to bring upstairs to test it. The meter works, as the needles moves is i touch the probes together.
http://www.drillspot.com/products/118847/Simpson_260-8_Analog_Multimeter?s=1

same meter but i bought mine dirt cheap on ebay

but just like on the fluke 289 cap testor i get no change.

Ahh, ok, it is analog, perfect.
The cap is dead, and since you mentioned the motor was hot, it was trying to start but the cap is dead so it does not spin.
Just to make sure, do a resistance test on the motor start and run windings to common just to make sure the motor is good. Then write down the ohm readings for each.
Then put the probe on the start and run terminals and you should get a resistance equal to the sum of each if the motor is good.

 

[tonydanzah]

alright the neighbor had an hvac buddy that let me buy the cap off his van. I put it in and the motor fired right up. Who knows how long the 22yr old motor will last after running with a blown capacitor.

 

[oltruckag]

alright the neighbor had an hvac buddy that let me buy the cap off his van. I put it in and the motor fired right up. Who knows how long the 22yr old motor will last after running with a blown capacitor.

I change caps in condensing units all the time that have been running (well, humming and tripping on internal overload ) with bad caps. I'm sure it shortens the lifespan of the motor, but they usually fire right up and run fine for years.

Glad it was a cheap/simple fix.