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Old 06-18-2009, 09:44 PM   #1
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AC blower short cycling-works on heat though


I came home from work today and my house is burning up ac isnt working right. The compressor seems to be running fine, when the blower does come on for a short time (at most 30 secs) the air is cold. Most times it just runs for about 2 seconds and shuts back off.

I tricked the thermostat into thinking it was cold and turned the heat on, at the lower speed the blower comes on and runs fine.

My 1st question is, can I just flip a wire around so the blower will come on at the heater speed till I can replace it?

2nd, since everything seems to run fine with the furnace should that lead me to just assume its the hi speed setting on the blower and replace the blower, or does that not rule out other relay's etc being the problem?

I took a picture of my wiring diagram, but am having problems getting it uploaded.

On the diagram I see there is a Hi volt terminal board with 5 connections (4 used)
C / HI / M HI / M LO / LO (not used)

The wires off this to the blower in order are
White to C
Black to HI
Blue to M HI
Red - to M LO
LO no wire

all those wires run to the blower motor

Would it be ok till replacing the motor to just run the blue wire to HI leaving the black disconnected? And would this make the air run just with the blower at the lower heater speed?

The Furnace is a "Tempstar Hi Boy" model 867-766022.

Thanks so much for any help
Steve

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Old 06-18-2009, 10:19 PM   #2
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AC blower short cycling-works on heat though


as a temporary measure yes. but don't be surprised if the blower dies completely in a very short time.

is your filter clean?

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Old 06-18-2009, 11:21 PM   #3
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AC blower short cycling-works on heat though


Thanks HVAC--Yea it was clean--took it out for now and had a fan blowing through the return.

Now suddenly it's working, from 102 when I got home from work Im now down to 83, and the blower is staying on steady now (didnt swap the wires it just started working.

Makes me wonder if:

It could have something to do with the compressor since its nighttime and has cooled down.

Or the evaporator since I had a window fan in the return air duct blowing across it constantly.

Really confused now.
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Old 06-19-2009, 06:09 AM   #4
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AC blower short cycling-works on heat though


Is your thermostat an older round one.
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Old 06-19-2009, 04:09 PM   #5
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AC blower short cycling-works on heat though


Hey Beenthere

No its a square one with the contols on top and temp lever on the side-- It says "White-Rodgers" on it.

Now that it's hot again it's back to short cycling--I guess Im gonna flip that wire, see if it works ok like that and if it does that tells me it's the blower thats the problem.

If that doesn't "fix" it:
If the evaporator was dirty would that potentially cause this problem? Im a little nervous about tackling cleaning it myself, but too tapped to have someone come out to troubleshoot the system/clean it etc.
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Old 06-19-2009, 05:02 PM   #6
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AC blower short cycling-works on heat though


Its probably not the wires your thinking of moving.

Its probably your thermostat.
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Old 06-19-2009, 05:31 PM   #7
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AC blower short cycling-works on heat though


Thanks Beenthere,

I can see that the mercury switch in the thermostat is making contact, it makes a little spark, and hear something switch (fan relay?) at the furnace when it does. It also switches (makes a clicking noise) when I turn the thermostat off--or turn it above room temp. It's the same noise the safety button on the front cover makes when you push it, but most of the time the fan isn't starting at the same time.

With the relay being tripped consistently, I would think that would rule out the thermostat, then again I don't know much about this stuff so I could definitely be missing something. Does it still sound to you like the thermostat is the likely culprit?
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Old 06-19-2009, 05:33 PM   #8
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AC blower short cycling-works on heat though


Stat, or your furnace board.
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Old 06-22-2009, 12:24 PM   #9
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AC blower short cycling-works on heat though


Figured I'd update this incase anyone has a similar problem. Turns out it was just the blower motor. I was about to go get a multimeter and start testing stuff then I decided wait a minute....I bypassed everything in the system and just plugged the hot for the blower into the door safety switch and it still didnt spin up so I figured it had to be the blower or the capacitor.

I went to expert appliance online and they wanted $98 for the capacitor, thanks to you guys I knew it was supposed to be a cheap part and went to Grainger down the street and got one for $5.40. Still didnt work, so I grabbed a blower motor and it's running great now.

Thanks again,
Steve
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Old 06-22-2009, 01:09 PM   #10
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AC blower short cycling-works on heat though


Quote:
Originally Posted by Steve60007 View Post
I went to expert appliance online and they wanted $98 for the capacitor, thanks to you guys I knew it was supposed to be a cheap part and went to Grainger down the street and got one for $5.40.
No wonder the HVAC business gets such a bad rap!
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Old 06-22-2009, 01:27 PM   #11
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AC blower short cycling-works on heat though


Quote:
Originally Posted by beenthere View Post
Its probably not the wires your thinking of moving.

Its probably your thermostat.
what males you think the hi speed winding is not gone in the motor been?
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Old 06-22-2009, 03:25 PM   #12
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AC blower short cycling-works on heat though


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what males you think the hi speed winding is not gone in the motor been?
Just ran into so many stats that the internal switch was cycling the fan when it got hot.
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Old 06-22-2009, 03:30 PM   #13
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AC blower short cycling-works on heat though


Diff regions diff condition i guess.

I have only come across the windings being bad.
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Old 06-22-2009, 03:39 PM   #14
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AC blower short cycling-works on heat though


We'll see in a day or so.
If he doesn't come back saying its doing it again. It was the motor.

If he has problems again, its the stat, and he wasted money on a blower motor.
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Old 06-22-2009, 04:00 PM   #15
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AC blower short cycling-works on heat though


i had three Honeywell digital mess me up on a smart valve system this last winter.

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