Furnace heats air but doesn't blow it out

[Tony0352]

When I kick the heat on, the furnace heats air but doesn't blow it out. The fan works when I kick it from "auto" to "on" (to blow in air from outside). If I've had the heat on before switching it to "on," hot air comes out at first, indicating that the furnace IS heating air, just failing to blow it out. Since the fan runs no problem when I switch it to on, I'm assuming the problem is with the relay, or the fan and limit control. I know little on the topic. Am I on the right track here? My furnace is a Janitrol electric (can't find a model number, house is 17 yrs old). I tried flipping breakers, and inspected the wiring (everything looks good). Thanks for your help.

-Tony

[heatseeker]

gas or electric heater? If gas there will be approx. sixty sec delay for fan to come on. If the flames go out yes you have a problem. On electric heater prob. a relay.

[surenuff]

bad heat sequencer

[DangWangi]

I too have a similar problem. When I have the thermostat set to "ON" everything works fine. When I switch it to "Auto" the gas flames stay light but the blower stops. I believe it is due to the furnace itself because I notice a slightly high whine that wasn't there before...just not sure how to troubleshoot the matter. Any thoughts?

[MTI STUDENT]

Turning the fan switch to on on the thermostat turns on the High speed of the fan , if the low speed is not working it could be a fan limit switch , find the two lead coming of the limit side if its a older furnace and see if you have power passing through if you test both wires while connected and are receiving power to the limit you will get a reading of 0 volts ac , if you read 120 v the limit is bad, if you get a 0 v reading then please check each side of the limit one lead on one side of limit and the other to case ground , this will confirm power is present.

[heatseeker]

Mti student- residential furnace will have 24 volts to the high limit switch. If it is real old say 1980ish it will have one of those fan limit switches that you can set the limits they will have 120 volts thru the fan side but those are far and few between.