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This is a down flow unit. There is no pressure valve on this unit. Here is all the parts on this unit.
1. Manual - reset, when used.
2. Blower and blower motor
3. Relief box also known as a exhaust flue.
4. Gas valve control knob or electric switch, ON/OFF
5. Gas Valve
6. Gas burner
7. Ratting plate
8. Blower door safety switch
9. Blocked vent safeguard tube and switch
10. Gas Manifold
11. Manual limit switch (2)
12.Hot surface ignitor
13. Flame sensor
14. Inducer blower motor
15. Control board with relays and transformer.
That is all the parts. The first thing the heater gets a call from the thermostat to the control board marked W. The board sends 24v to the inducer fan relay which makes and causes the inducer fan to come on now there is a small tube that runs from the inducer fan box to a switch when the switch makes it sends power to the board which proves you have cleared the exhaust flue then the flat surface ignitor starts to glow and then gas valve opens and fires. now if this tube is stopped up the heater will not fire and will lock the unit out. Also if the flue is stopped up with trash it will do the same thing. If you are not familiar with gas heating units you should call a service company out and check out the system there is a lot of things that need to be checked out every heating season as to keep you and your family safe.
There are several limit switches in the unit there in various places in burner compartment. One on blower housing . One thing that I would try is replaceing your filter and turn the power off to the furnace and try starting the system after power is D/C for 5 minutes.
Hello, looks like you limit switch keeps opening because your furnace is overheating, Check your air filter and blower wheel to make sure it is not dirty and make sure you blower motor is moving at the proper speeed. Usually when air flow is cutoff the limit switch will open.
The symptoms seem to be related to the main blower motor and/or it's capacitor. Turn the system off for a couple of minutes and then turn just the fan on while the thermostats heat setting is in the off position. If the lights still dim then replace the motor and capacitor. The clicking noise is the fan relay.
limit switch is on the heat exchanger black plastic about 1and1/2 in. by 2 in. with 2 wires going to it , it has 2 screws holding it in take it out and check it with an ohm meter and you should not have a reading if it is good
A constant red light (not blinking) indicates that the thermostat is not calling for heat. Of course you know it is but just to be safe, jump out R and W on the board. If it continues to do the same as you indicated, replace the board.