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-   -   AC blower short cycling-works on heat though (http://www.diychatroom.com/f17/ac-blower-short-cycling-works-heat-though-47000/)

Steve60007 06-18-2009 10:44 PM

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

hvaclover 06-18-2009 11:19 PM

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

is your filter clean?

Steve60007 06-19-2009 12:21 AM

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.

beenthere 06-19-2009 07:09 AM

Is your thermostat an older round one.

Steve60007 06-19-2009 05:09 PM

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.

beenthere 06-19-2009 06:02 PM

Its probably not the wires your thinking of moving.

Its probably your thermostat.

Steve60007 06-19-2009 06:31 PM

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?

beenthere 06-19-2009 06:33 PM

Stat, or your furnace board.

Steve60007 06-22-2009 01:24 PM

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

sktn77a 06-22-2009 02:09 PM

Quote:

Originally Posted by Steve60007 (Post 291214)
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!

hvaclover 06-22-2009 02:27 PM

Quote:

Originally Posted by beenthere (Post 290048)
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?

beenthere 06-22-2009 04:25 PM

Quote:

Originally Posted by hvaclover (Post 291251)
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.

hvaclover 06-22-2009 04:30 PM

Diff regions diff condition i guess.

I have only come across the windings being bad.

beenthere 06-22-2009 04:39 PM

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.

hvaclover 06-22-2009 05:00 PM

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


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