Hvac anyone?

[pr_capone]

I've got a Coleman furnace that has decided that it will only blow cold air. The house is at 68 degrees.

Any ideas? Is there a pilot like on a water heater that I can check for? It is gas.

[Boise_Chief]

It's kind of tough to tell you from 500 miles away but I'm guessing it's one of several possible things.

Take your doors off the front, there will be a switch that you need to tape down for it to run. Turn off your thermostat for 10 seconds or so and then turn it back on. go to your furnace and let me know what happens. do you see a glow after about 20 secs and does it try to light. Is the combustion motor running, it's the little motor behind the cover you will be looking at the end of it.

It's probably one of these things:
Bad transformer 110v - 24v
Combustion motor not running
thermostat bad ( batteries, not prog correctly likely)
bad igniter or flame sensor

[Chief Roundup]

Man this could be a lot of different things. If you have never had it serviced the burners could need to be cleaned which can cause the flame to roll out of the heat exchanger and hit a safety switch.

When you make the thermostat call for heat after it has been off does the inducing motor run?

Does it have an electronics control board with a light on it? If there is and it is blinking count the flashes. The pauses might seperate 2 numbers. There should be a label on the door that will tell you what the flashes mean.

[Boise_Chief]

hehe just so your code for the limit switch.
Change your filters...
there is a sensor that goes into the airbox probably on the right side should have 2 wires going into it. there may be a little reset button to hit to reset it. your furnace can't breathe correctly. It is not getting enough airflow or it is over heating. You may also have a small rubber hose going to an airpot pull off the hose and us a little bit of wire like a paperclip and clear the rust that is blocking it inside the limit switch.
Should be one of those.

[Chief Roundup]

Originally Posted by pr_capone

Ok... don't have a model number but I have more information. Looked at the inside of the door there and there is a fault code.

I see a red light flashing 4 times which indicates "limit switch open"

what does that mean? lol

A Limit Switch is a safety mechanism. You should have a professional come look at it in person.
Limit switch tells me that you have had the flame roll out of the heat exchanger or the heat exchanger is getting to hot.

I think your furnace is being choked for air. You may need to build a little air ramp so air can get into your furnace. Do you have any kind of experience building ramps?

[pr_capone]

Wierd.

Ok, so I opened up the furnace and it has a button on the front. I push and hold the button and everything fired no problem. I can see the blower turn and I can see 4 gas jets kick on and turn to flame. Seems like the furnace itself is ok...

I replaced the batteries on the thermostat but now I can't get the fan to kick over from the thermostat.

[Chief Roundup]

Originally Posted by Boise_Chief

hehe just so your code for the limit switch.
Change your filters...
there is a sensor that goes into the airbox probably on the right side should have 2 wires going into it. there may be a little reset button to hit to reset it. your furnace can't breathe correctly. It is not getting enough airflow or it is over heating. You may also have a small rubber hose going to an airpot pull off the hose and us a little bit of wire like a paperclip and clear the rust that is blocking it inside the limit switch.
Should be one of those.

Yeah if it is a high limit you could have a restriction and you should change your filters every month on average.

[pr_capone]

Originally Posted by Phobia

I think your furnace is being choked for air. You may need to build a little air ramp so air can get into your furnace. Do you have any kind of experience building ramps?

I need you to ban yourself from this thread now.

[Boise_Chief]

There are 2 limit switches on a furnace. 90 plus percent of the time it is dirty filters not allowing enough air flow or rust inside the switch from condensation. On a 5 year old furnace I would be shocked to have a problem with the heat exchanger. take a pic of the front without the covers on.

[Chief Roundup]

Originally Posted by pr_capone

Wierd.

Ok, so I opened up the furnace and it has a button on the front. I push and hold the button and everything fired no problem. I can see the blower turn and I can see 4 gas jets kick on and turn to flame. Seems like the furnace itself is ok...

I replaced the batteries on the thermostat but now I can't get the fan to kick over from the thermostat.

I know you will but be sure to watch it and if it does it again do not reset it because that indicate you have a problem. Then call a technician.

[Boise_Chief]

taking the cover off cut power to the board and reset it. Is your cover on now? don't forget to check the filters it will probably happen again unless you figure out what was reducing the airflow problem.

[pr_capone]

Tell you what... I guess these things are like computers. Opened the lid, pressed the last error code button and nothing showed up. Changed the filter and put the lid back on and now everything if firing on all cylinders.

Odd but I'll take it. IF it goes down again I'll be sure to call an hvac tho. The assist is much appreciated for this (less than)HandyMan.

[Titty Meat]

Ask Bugeater he knows his shit.

[Boise_Chief]

Another thing that could effect it is if you have shut down the vents in multiple rooms.
Good luck.

[mikeyis4dcats.]

bad filter...it worked with the panel off because it was pulling air direct from the room