Frigidaire furnace FG6RA 096C-16B comes on ignites starts to blow then 3 amp fuse blows replace it fuse blows as soon as power is on. Help

The problem is most likely in the thermostat wire between the air handler and the thermostat or even outside at the AC condenser unit. the 3-amp fuse is protecting the circuit board from burning out. I recently saw this on a furnace blowing a 5-amp fuse due to the AC compressor had the thermostat wire running through a chassis knock-out hole with no protection. The thermostat wire was grounding out to the metal chassis. I detected this by testing each thermostat wire at the furnace circuit board for resistance (Ohms to ground). Remove each wire one-at-a-time and test that wire with one meter probe while the other probe lead is grounded. If I recall correctly the Ohms on the faulty (grounded) wire was less than 5. Using Ohm's Law formula v=iR and a 24v control voltage you can see that 24/5=4.8 amps. However, the control voltage actual RMS on my meter was near 29 volts, so the fuse would definitely blow for a leak to ground with 5 Ohms resistance. The problem is most likely in the thermostat wire between the air handler and the thermostat or even outside at the AC condenser unit. the 3-amp fuse is protecting the circuit board from burning out. I recently saw this on a furnace blowing a 5-amp fuse due to the AC compressor had the thermostat wire running through a chassis knock-out hole with no protection. The thermostat wire was grounding out to the metal chassis. I detected this by testing each thermostat wire at the furnace circuit board for resistance (Ohms to ground). Remove each wire one-at-a-time and test that wire with one meter probe while the other probe lead is grounded. If I recall correctly the Ohms on the faulty (grounded) wire was less than 5. Using Ohm's Law formula v=iR and a 24v control voltage you can see that 24/5=4.8 amps. However, the control voltage actual RMS on my meter was near 29 volts, so the fuse would definitely blow for a leak to ground with 5 Ohms resistance.

Thank you. I had discovered that it was the thermostat wire prior to reading your answer but you were exactly right. I put on a new thermostat wire and it's working great Thank you. I had discovered that it was the thermostat wire prior to reading your answer but you were exactly right. I put on a new thermostat wire and it's working great