Ruud rooftop package electric ac gas heat unit--heat comes on intermittently

The heater in our 25-year-old Ruud package unit sometimes doesn't come on. We hear the loud flat hum of a motor(?) but we don't hear the undulating sound that precedes the heater kicking in. It seems as if the heater won't come on first thing when it's cold outside, but we can get it to come on later in the morning. The capacitor has a 2009 date, so it looks like it's been replaced. Would appreciate any ideas. Thanks.

 

You should post the model and serial number or at least a picture. Search the net for a manual, it will likely have troubleshooting information. It is possible that the electric motor is old enough to be the kind with oil ports, if so it may need oiling. The manual would have the maintenance info in it.

 

Had this same issue...kinda. You need to find out if the igniter is firing up the burners. The first sound is probably the draft inducer motor. If it just hums w/o running...prob the motor has failed. If it runs, but you see no spark or glow from the igniter...(most times spark on these), then it could be a pressure switch or the igniter module.

The way it works is...inducer runs... pressure switch is satisfied...module sparks...burners light..once heat is right blower turns on.

Depends on your skill level...but you may be able to narrow it down just by careful observation with the cover off so you can see everything.