short in wiring

Stop blowing fuses and use a test light. When the light goes out you have removed the issue. Then you need to remove items systematically to identify where the problem exists. Easy to disconnect components to isolate the issue to be in the component or wire. Tracing an issue in the wire through inaccessible areas could prove difficult.

if you have a suburban furnace the wires have a plug in at the furnace unplug it and see if fuse still blows.

A picture of the fuse and its location may be useful, too.

A/C unit is coleman mach thermostat on wall is coleman also

My converter only charges my batteries. From there the 12 volts are sent wherever it is needed. The fuses on my converter protect it from miswiring and/or reverse polarity from the incoming 120.volt system.
Good Luck and stay safe.

Hello trm3650 and Welcome!

Post Brand/Model of A/C Unit and Furnace and type of thermostat

15A is MAIN DC for controls
Typically that FUSE would feed DC directly to furnace and it then gets triggered by DC back from thermostat to start furnace FAN
Some designs have the DC going to a control module in A/C Unit

SO Bran/Models will be helpful


** I grew up in Casper
Went to East Jr High, Dean Morgan Jr High, Natrona County High and then Kelly Walsh where I graduated (Dad was oilfield and we moved to/from/back to Casper a LOT!)