It's common for HVAC systems to be improperly designed. It's also a common misconception that it's okay to close vents. If a regular density filter is restricting airflow (and causing the unit to heat up too much and trip a safety switch) then you need to do something about the airflow.
In general it's not a good idea to close vents because it changes the "static pressure". I don't know the details but basically you don't want the pressure in your vents to be much higher than the pressure in your house. If so the fan is working too hard and there isn't enough air passing over the heat exchanger.
Diagnostic Display
According to the Installation Instructions, your model is equipped with a diagnostic display.
To review the any error codes:
Press the diagnostic push button and hold it to cycle through a menu of options. Every five seconds a new item will be displayed. Release the button when the desired mode is displayed.
When a solid "P" is displayed, the furnace capacity/size is programmed.
When a solid "E" is displayed, the control enters the Error Code Recall mode.
Error Code Recall mode menu options:
- No change (displaying error history) remains in Error Code Recall mode.
- solid "b" exits Error Code Recall mode.
- solid "c" clears the error history. Must press button while flashing "c" is displayed to clear error codes.
When the solid "-" is displayed, the control enters the Field Test mode.
Field Test mode menu options:
- Solid "C" starts pressure switch calibration.
- blinking "-" exits Field Test mode.
Firing Sequence
If you don't want to get into all that, you can simply use the firing sequence to try and troubleshoot the problem. Start by turning the breaker, and any serviceman switch on. Next turn the thermostat up, until it calls for heat.
First, you should hear a small click, ping, ding, or some other sound, to indicate the gas valve opened (may be too quiet to hear on some valves). Next you'll be able to hear a quiet hiss, as the gas starts to flow. The ignitor; either a spark gap or hot surface, will turn on. You'll either hear a rhythmic click-click-click, or see a small bit of metal turn red. At the same time, the draft inducer should turn on. This may be quite noisy, and could make diagnosing problems by sound difficult.
No Flame
If a flame is not sensed within a few seconds (may be variable depending on model), The gas valve will close, the ignitor will turn off, and the draft inducer will purge the system for 15 seconds (may be variable depending on model). The sequence should repeat again, for up to 5 tries (may be variable depending on model). If after the 5th try, there is still no flame. The system will purge for 20 seconds, then shut down and display and error code.
Flame
If a flame is sensed, the furnace will wait for the flame to stabilize. Once a good flame is detected, the indoor blower should start, and warm air will be blown throughout the house.
Best Answer
If you follow the (3) wires from gas valve, two end up on the control board and one goes to a limit switch on the blower. This limit switch was burnt out on my furnace. It's a relatively inexpensive part to replace. Good luck.