OWB going and then the air conditioner turned on

[DSS44889]

Not really sure what is going on here. Currently I control the temperature
manually from the main furnace thermostat, I was planning on adding a
second thermostat to run just the blower this weekend. On Monday I
turned the fan back to manual and the furnace didn't turnoff and the strange
thing is that the air conditioner turned on. Whatever I do short of tripping
the breaker doesn't turn the furnace off. I did turn the air conditioner off
so I don't have that running. My water temp. coming in is 185, same as
last year. I really have no idea what is going on, do I need to get a HVAC
person out to correct this? If anyone has an idea what is happening I would
really appreciate a solution to this.

Thanks and have a GREAT Thanksgiving!!

Dave

 

[KsWoodsMan]

We've had a bad thermostat do this. It controled whether the air runs or the gas valve. If it fails it can keep one or the other running.

Time to install that new one you been looking at.

 

[projectsho89]

You did switch the thermostat from COOL to HEAT, didn't you?

As long as the FAN is set to MANUAL, the blower will run. A blower that is running doesn't equate to a furnace that is running.

Perhaps you might wish to clarify details some more.

If the settings are correct, disconnect the yellow wire from the thermostat. If the AC no longer runs, whether properly or improperly, the thermostat has failed (stuck contacts, probably).

Steve

 

[DSS44889]

The thermostat has the current settings:

System - off (no heating or cooling)
Fan - auto

But the blower is still running. This is a Lennox furnace and thermostat which
the builder installed. Last season this setup worked without any problems.

The only thing I've done is run a second thermostat wire so I connect a
thermostat to control just the blower. This wire isn't connected to anything,
just nailed to the floor joists.

Dave

 

[KsWoodsMan]

One of the first steps in diagnosing it is to determine where the problem is. Wheter it is the controller ( thermostat) or the unit itself.

projectsho89 gave good advice. If the blower stops, it is the controller. If not, it is the unit. Might save $200 doing it yourself instreaa of calling a HVAC guy away from his family on a holiday weekend.

 

[stephen44]

try disconnecting this wire - in case anything is short ? - since that was the only change. Maybe - putting the thermostat cover back on - shorted something ?

 

[KsWoodsMan]

:agree2:

The thermostat has the current settings:

System - off (no heating or cooling)
Fan - auto

But the blower is still running. This is a Lennox furnace and thermostat which
the builder installed. Last season this setup worked without any problems.

The only thing I've done is run a second thermostat wire so I connect a
thermostat to control just the blower. This wire isn't connected to anything,
just nailed to the floor joists.

Dave

Is either end of the wire you ran connected to anything at either end ? This would have been a good thing to mention initially. Instead of

I was planning on adding a second thermostat to run just the blower this weekend.

If either end is connected to anything disconnect it , put it back as it was to start with before you made changes to a working system and see if the problem persists. Then follow normal diagnostic routines to isolate the fault to the controller or the unit.

Once it is corrected, then try to add the second thermostat if you chose.

 

[Wirenut2266]

I think it working ok.....

You need to replace t-stat. Wrong one for your application. You need one with heat/off/cool and your problem will dissappear. New one will still have fan auto/man. as well.

 

[DSS44889]

I might not have been clear or not.

Nothing has changed on the existing system. I haven't added or changed
anything. I was planning on adding a second thermostat to just turn on
the blower, nothing has been connected to the new thermostat or to the
furnace. I have only nailed a new thermostat wire to the floor joists. The
existing thermostat is a heating and cooling model. Do thermostats just go
bad?

 

[KsWoodsMan]

I might not have been clear or not.

Nothing has changed on the existing system. I haven't added or changed
anything. I was planning on adding a second thermostat to just turn on
the blower, nothing has been connected to the new thermostat or to the
furnace. I have only nailed a new thermostat wire to the floor joists. The
existing thermostat is a heating and cooling model. Do thermostats just go
bad?

Yes, electronics are known for it. Easy to see a fault with anything mechanical, electronics - not so easy. Most use componets that are just adequate for the application.

Have you pulled off any wires to determine if the problem is the thermostat or the unit yet ?

 

[DSS44889]

I pulled the thermostat off (it has pins which lineup with a mounting
bracket) and the furnace blower continues to run. Should I disconnect
the thermostat wires from the furnace? At this point I'm guessing that
I'm having a problem with the furnace itself, correct? Or is there something
else I might be missing?

Dave

 

[Wirenut2266]

hmmmmm

If you pulled t-stat off sub baseand unit still runs: You could have shorted wires with a staple and basically bypassed t-stat. Leave t-stat off sub base, go to furnace, disconnect wires from circuit board you wired, does unit turn off? If so, you shorted wires.....Remember, this is done with no-stat hooked up. If continues to run with wires off board, yup, bad board.....This should work unless i'm totally baffled at what you wrote......

 

[Scootermsp]

Breakers

At the end of the cooling season it is a great idea to shut off the breakers for your A/C condensor units so they CANNOT come on when the heating coils sre roasting your plenum. Doing so can damage your condensor units

 

[mtfallsmikey]

Or...a shorted t-stat subbase...Ask me how I know.