YORK DIAMOND 80 Series
Furnace comes on and then cycles,blower, heat and heater shuts down, then cycles again. after 3 cycles it shuts down and blows only cold air. blower never shuts down. You turn off the furnace then back on, it go's 3 cycles of heating and heat shuts down and blower blows cold air, blower never shuts down. feel it's caused by some type of safty switch, but which one and how to test it
Most likely the high limit.
It indicates, that either, the air filter is dirty and restricting.
Or, the A/C coil is dirty and restricting.
Or, you have blocked/restricted supplies or returns.
Or, you have alays had low air flow, and the limit switch is wearing out.