[mdm01]

I have a Tempstar furnace model number NUGS050AF01 - Serial # L1893714174 that recently started blowing cold air. The thermostat controls seem to be working because the AC side works fine and the furnace will start it cycle- but something is shutting it down. The draft inducer blower and large fan also work. I've replaced the 120V - 24 V transformer hoping this would solve the problem, since I could not get a 24 V reading off the terminals on the original unit. I've taking off the cover and cleaned bugs and debris from inside the area in front of the igniter and the supply air PVC piping. When I test the unit the igniter glows bright for about three seconds and then shuts off, after three failed attempts the White Rogers Ignition Control Module starts to blink.( This lock out timing is listed in the service manual under specifications that include:

Input rating BTUH - 50,000
Output rating BTUH - 48,000
Temperature Rise 15 - 45 degrees
Ignition Type/Model - HSI/50F47 - discontinued new model WR 50E47-843
Rated ext Static Press - .10 - .50
Lock Out Timing - After 3 tries


Is there a limit switch, pressure switch, and/or sensor that I could test that is controlling the gas valve and signaling it not to open?

[Grady White]

You need to find out if the gas valve is getting 24 volts during the time when the ignitor is glowing. Be sure to check the entire time the ignitor is glowing.

If you are not getting 24v, trace the wires through the various safety switches. Once you find 24v through a switch, the next one toward the gas valve is where the circuit breaks. For the sake of safety, I suggest shutting off the gas while testing.