I cannot find the filter and my furnace is not providing any heat. The limit switch is working fine as is the flame sensor. Diagnostic lights are: 1 slow bling 2 on Any clues? Thanks

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    Hello, and welcome to Home Improvement. Have you tried looking at the manual? – Daniel Griscom Jan 16 '19 at 22:44
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    What does "1 slow blin[k] 2 on" mean? – isherwood Mar 12 at 13:53

Usually the filter is placed in the duct just ahead of the coils. Look for a “wingnut” that can be removed for access to the interior of the duct.

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  • "Just ahead of the coils" isn't an ideal description. The intake plenum feeds air to the fan compartment, which then pushes it on to the air exchanger(s) and then any cooling coils above. Better to just say "upstream of the furnace" or somesuch. – isherwood Mar 12 at 13:56

A furnace filter is to be placed in the return air side of the blower. Occasionally the filter is in a basket configuration in the blower compartment. If it's not in the blower compartment it should be pretty obvious and easy to see. If you don't have a filter your installer should be liable to replace your unit because dirt builds up on the fan blades, gets into the secondary heat exchanger and if installed, in the air conditioner's evaporator coil. Filters are an absolute requirement on a forced air system. The flash code is indicating high limit switch open. So she's too hot. Plugged filter will definitely do that. No filter means she's garbage, or at least needs to be torn apart and thoroughly cleaned.

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  • Filters in that type of furnace are usually not inside the furnace cabinet. This is important to point out. Folks commonly root around behind the covers looking for them. Look in the supply duct plenum for a panel resting on top of a horizontal section. – isherwood Mar 12 at 13:55

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