Does anyone have an idea as to why the fan on my heater/AC would run
constantly when the thermostat is set to have the fan in "Auto" mode
but not run at all when in "On" mode?
The whole story:
My fan was running all the time regardless of thermostat setting,
including heat and AC off. I disconnected the green wire from the
thermostat and it kept running. From everything I read that indicated
a stuck fan relay. When I looked at the fan really it was cooked,
burned plastic, etc. So I replaced it with the same model. I'm
pretty sure I wired it exactly the same, I took notes, etc. So now I
got the weird situation described above. I picked up a new thermostat
thinking that maybe the burned relay took out the thermostat but it
does the same thing. That makes me believe I did screw up the wiring
but after much reading and checking and rechecking the wiring looks
right. Does any know what could cause this?
On Fri, 21 Mar 2008 18:10:34 -0700 (PDT), stoneattic
Well, it would have been best if you had figured out what ruined the
first relay. I don't know much about how these things are wired these
days, but it's very very unlikely the relay ruined itself.
I'll bet if you check the new relay, its contract points are fused
What would ruin a relay? Maybe it's a 24 volt relay but somehow 110
volts it getting to the coil?
Thanks for the reply.
I don't think the new relay is fused because if the relay were fused
wouldn't you expect it to run in both "auto" and "on" like it did
I checked and the relay is rated for 13.8FL @ 120 and 82.8LR @ 120.
The 24v side of it is hard wired so I can't screw that part up. :)
If 'stat fan control does not have an effect, logic control board in the
furnace went bad. Try to measure 24V on that relay primary(coil) if
there is 24V all the time with G lead removed at the furnace end not at
the 'stat to rule out shorted wire. then, well?
Depending upon the make and model of the unit, something other than the
thermostat is sending power to the fan relay. Some units use a delay timer,
which could be faulty, or shunted wires at the blower could cause it
You're right. You messed up on the wiring. Check the units blower door for
the mfg.'s wiring diagram, and compare notes. I think you'll find you've
mis-wired the relay. And BTW, if you're not careful, you will let ALL THE
FACTORY SMOKE out of the motor and it won't run at all.
I'm pretty sure something is not wired right, despite my best effort.
There is no wiring diagram in the blower units door unfortunately.
Assuming I have the thermostat connected correctly...
What I've got is..
power coming in (white and black and bare "ground")
red and black on the N/O side of the fan relay, a black and a white on
the coil of the relay
a blue and a white going to the oil burner motor
a red, an orange, and a black going to the fan limit control
If I had a diagram I'd be all set :)
There in lies the problem. There's no diagram to be found.
I'm thinking that the fan limit control may be bad as well, but until
I get it wired correctly I won't know.
On Sat, 22 Mar 2008 16:27:49 -0700 (PDT), stoneattic
I hope you are not holding your breath while all this is going on.
Intelligent people know when to say when. I think you pass that point
quite a while back. Certainly your time is worth something? Its time
to break open the piggy bank and get it done right, get it done
quickly and get it done with a warranty.
I figured it out. :)
It was a wiring mistake on my end. I just started from scratch. My
mistake was trying to figure out the problem with the way it was
currently wired. I just disconnected everything and work the wiring
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