blower won't turn on in AUTO

nhpick02

also, it looks like i have two different limit switches...a single pole and a double pole. since i am showing 124 volts on all connections of the limits does that mean they are probably ok?

beenthere

Many systems use 1 speed for heating and another for cooling.
If yours does, you will see a connector marked cool, and and another marked heat. On the control board.

J_theo

Bad circuit board. If it runs in the "on" position, but during a normal call for heat cycle the flames light and go off after about 66 seconds, you have a bad circuit board. If it's a carrier 58MXA or 58DHC, they're notorious for failed boards with that exact problem

nhpick02

ok I'll see if I can find that. Is the control board something that looks like a computer chip? I haven't seen anything like that on my system.

J_theo

if you open the blower compartment, you'll see what appears to be like you said, a big computer chip, follow your t-stat wire and it'll lead you right to it (inside the unit) it'll either be a dark brown, polished black, or pale white board, on the board you'll see your t-stat connections as well as about 15 other larger wire connections, that's your board. However, if your unit is older, you'll have what looks like a transformer with about 12-15 metal pegs sticking out of it, that is your fan relay DO NOT TOUCH IT without making certain the power is off at the breaker and service disconnect. If it's not a board, it's a relay, a board will show subtle signs of burn or capactior breakage in the back of the board, you'll need a new one. A relay is about 15 bucks from any supplier, if you have one, probably wouldn't be a bad idea to replace it either way

nhpick02

ok but my furnace is an electic unit. It's a nordyne feha-015ha-01 and it's in a fleetwood mobile home, and I don't think it has any type of control board unless I'm missing it. I don't know if it helps but it was really cold when I tried to start it up and some steam came from inside the unit maybe from some condensation that was in there...ixwonder if that could have fried something.

nhpick02

ok I have already replaced the fan relay, as well as the sequencer.

J_theo

Are you aware of the location of the heating elements? where does the t-stat wire go? it has to enter the unit somewhere, trace out the wire. I'm pulling a schematic on your heater now

nhpick02

The thermastat wires come in and hook up on top of the control box which has the fan relay, the auto/on switch, the hear/cool switch, and a couple other boxes. The heating elements are down on the bottom of the unit, and that's where the limit switches and sequencer is.

J_theo

it's got to be either the relay isn't transferring the power correctly and stepping up or down voltage, the sequencer isn't making, or the heating element isn't getting hot enough to call for the fan relay to close causing the fan to come on.

NYCtinman

The heat & a/c run @ different speeds on direct drive systems - you can jump out pressure switch(s) before replacing them - your best bet would be to call a service tech - you could spend more money in the long run

hoistdoctor

On some mobile home systems, the A/C and heat have different control power sources. If you look at your condensing unit outside and it has a transformer in it then your transformer in the electric furnace could very well be bad. You did say you had 240 volts on the primary and nothing on the secondary. Also many times the blower speed for heat is slower than for A/C. The motor has more than one run winding and if it runs in high speed its probably ok but not guaranteed to be good for a slower speed. I would check the transformer secondary again and if you get 24 volts then check power to the motor on the lower speed. The limit switches are for cutting out the elements if the blower fails to run to keep the furnace from overheating