EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Rick Law on March 04, 2014, 02:04:19 am
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Guys, I can use some suggestions.
I have an HVAC furnace with a blower problem. It hums and sometimes starts while other times it does not. When it fails to start, If I give it a good spin it may start.
My initial guess was the capacitor. So, to get heat in the very cold night, (-10C to -15C at night) I purchased one in electronic store a few towns away - paid an arm and a leg for it. (7.5uF, 370V).
It did nothing. The motor still needs a spin start and it still hums. The new cap measures exactly 7.5uF on my UT61e while the removed old 7.5uF measures 8.6uF.
I know if I take it back to exchange for a different one, the guy will measure it with the DMM and point out that it is good. I need to do a "second level test"... Any suggestion on how I should further test the capacitor to see if it is really working?
(I understand there may be other problems, I just want to rule this one out first...)
Thanks for your input.
Rick
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If it's a cap start, induction run, it's possible the switch is gone as well.
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If it's a cap start, induction run, it's possible the switch is gone as well.
Frankly, I don't know if it is a cap-start or not. Outside of reading the motor's part number, what is the best way to determine that? (I can't get to the motor without moving a whole bunch of things - but I can get to a wiring diagram / schematic on the covers I can removed.)
As to the switch, can you tell me what switch are you referring to?
I do have a secondary (and a third) worry perhaps exactly due to a switch - I do hear some sound like a relay-chatter when the heat part have the motor running and I turn the fan switch on as well. This relay-chatter sound however has a "deep voice" sounding almost like a low volume hum but at different audio frequency to the motor hum. This "deep voice" chatter also come from the motor compartment. The fan-switch should be redundant as the heat already have the fan on and it should merely do nothing.
Thanks for the help.
Rick
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Most small HVAC blowers around here are PSC (permanent split capacitor) motor (http://en.wikipedia.org/wiki/AC_motor#Permanent-split_capacitor_motor)s.
What brand and model of furnace is it?
What does the wiring diagram show for motor connections and/or model info?
I do hear some sound like a relay-chatter when the heat part have the motor running and I turn the fan switch on as well. ... The fan-switch should be redundant as the heat already have the fan on and it should merely do nothing.
The fan switch might try to run the motor at a different speed than for heat (i.e. using a different set of motor windings).
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Most small HVAC blowers around here are PSC (permanent split capacitor) motor (http://en.wikipedia.org/wiki/AC_motor#Permanent-split_capacitor_motor)s.
What brand and model of furnace is it?
What does the wiring diagram show for motor connections and/or model info?
I do hear some sound like a relay-chatter when the heat part have the motor running and I turn the fan switch on as well. ... The fan-switch should be redundant as the heat already have the fan on and it should merely do nothing.
The fan switch might try to run the motor at a different speed than for heat (i.e. using a different set of motor windings).
You are right on for both counts, Mr. Dfmischler!
It is a PSC Blow Motor - It is right on the wiring diagram and I thought PSC is the motor's brand name! Dummy me. And, indeed the fan switch is connected to the blue/medium instead of the high as when heat is on.
The furnace is a Borg Warner model P3USD16N10501A.
I now think the motor is the fault - since I started hearing squeeking when the fan-cylinder is spinning while I turn it to try a "spin start" and sometimes it hits a rough spot and the wheel has a hard time turning.
I bid the bullet, move a ton of junk out of the way, and got the motor assembly out. I thought getting the assembly out was the hard part... Now I can't get the fan-wheel off the blower motor. That fan wheel-hub is holding on so damn hard. I know I can get a hub puller, but spending $60 for a hub puller rather defeat the purpose of DYI to save a few bucks...
Anyone knows a good trick? I am open to suggestions. I am thinking some WD40 first, and if that fails, try blow torch.
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For small motors hold the fan or pulley between your legs and hit the motor shaft with a hammer and a piece of hard wood or brass or aluminium drift.
For larger size use a metal bar with a hole in the middle a bolt and nut and strong fence wire to make a puller.
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Make sure all set screws are loose, or out (there are often two, 90 degrees off from each other). Tapping the motor shaft out as G7PSK said will probably work, but pay attention to what he said about using wood or aluminum as the striking surface so you don't mushroom the end of the shaft and wedge the hub. Sometimes levering against the motor housing works at some point, but you need to spread the forces so you don't bend the blower wheel.
You might just have a bad bearing on the motor, but I haven't found a good local source for the right kind of bearings, and it's not a good time of year to have your only heat source down. Last time I had a blower bearing problem in one of the unit heaters at my workplace I bought a motor, and replaced the bearings in the old one at my leisure so now I have a spare motor. I have 7 unit heaters that use that same motor.
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... and it's not a good time of year to have your only heat source down ...
I lived in New Jersey for about 20 years now, this is the coldest year I have encountered. I don't recall seeing any -10F and it was like that a month ago. I lost the heat less then a week ago. Last few days, it was -1F to -4F coldest - better, but of course it is no fun.
Now if you would allow me, I need to rant!.
I thought having no heat was bad, but it can get really much worst... Early this evening (before it even gone below freezing), the pipe to the garden spigot burst. So, I have neither water or heat now. Worst is, the part of the basement (with pipes to the outside) is finished as a rec-room so all the pipes are hidden. I will have to cut the dry wall(s), find the pipe, cut and put a cap on that pipe before I can bring water back. The guessing game now begins (guessing where the pipes branch off to the bath rooms and the outside) since I don't want the bathrooms to be without water.
My basement (where my work area is) is about 40F lowest, and the burst occurred in the late afternoon/early evening before it went below freezing. Still, I wonder if the cold inside has anything to do with that.
So, I have to put that damn fan-wheel aside, do some wall cutting, do some pipe-soldering... I need water more than I need heat for now.
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Just want to close this off and thank you for your suggestions. I removed the steel hub and separated the motor from the fan successfully.
Thanks for all the suggestions. I applied WD40 twice a day for two days, hammer it via a wood dowel each time I applied the WD40. By third day, it started giving a little and finally it came out. Having the motor allowed me to see the specs on the motor, found a replacement (and waited, and waited for the shipment to get here)... and now life is good again.
It was rusted on so hard I think the hub-puller (which I was reluctant to get) would have had a very very hard time anyhow.
Thanks, guys.