DIY Home Improvement Forum banner

AC blower short cycling-works on heat though

10204 Views 14 Replies 4 Participants Last post by  hvaclover
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
See less See more
1 - 5 of 15 Posts
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.
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.
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?
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,
1 - 5 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.