Heat Pump Unit

Low refrigerant levels (most common cause.)

it sounds like your outdoor unit is running, but the AC is blowing out hot air, start with cleaning the condenser coils. Spray the coils with a water hose, clearing away the loose dirt and foliage. If the AC continues to blow warm air, call an HVAC expert for help with refrigerant levels.

Make sure you have power to the outdoor unit. The outdoor unit on a minisplit powers the indoor unit.

Heat pumps defrost which is the AC mode, if the heat strip isnt working during a defrost, the air will be cold, A heat pump only feels warm if the heat strips are on too! the refrigeration cycles heat output is much less sensible to our 98F skin. heat pumps that satisfy a room setpoint are working at least, all heat pumps feel drafty to most.

Red wire goes to Rc with a jumper wire to Rh
White wire goes to W
Green wire goes to G
Yellow wire goes to Y

You have a low voltage short in the thermostat wires or the coil of a relay or contactor.
Best thing to do would be to remove all the wires to the outdoor unit (be sure to mark where they go... may only be 2 wires if you don't have a heat pump) and try turning the system on. If it doesn't blow the fuse, you know the short is between the indoor and outdoor units. Start hooking the wires back up one by one, that way, when the fuse blows again while you're putting the wire back on, you'll know which wire is shorted.
If the fuse still blows you will know it's in the wiring between the thermostat and indoor unit. At the indoor unit, disconnect all the wires to the thermostat except for the ones that go to R and C (these are the 24v wires). Now, with the thermostat calling for heat or cool, hook one wire up at a time starting with G, then Y, then W and see which wire causes the fuse to blow.
If it's G, it could be the thermostat wire or the fan relay. If it's Y or W, the short is likely in the thermostat wire between the indoor unit and thermostat. If that's the case, visually inspect the wire for damage and cut and splice if necessary.

Sounds like compressor not running. may be a bad capacitor, could also be low on freon.

There could be a couple of problems going on. Your fuse on the heater up in the attic is popped.
Your glow ignition is broken.
Your spark ignitor is bad (if that is what you have)
GAs valve is bad.
Or the vent sensor is bad, meaning that the exhaust fumes are not going anywhere.
Now when you turn on the heater your condensiing unit outside should never turn on unless you are calling for AC. Now if the ac is not coming on there can be more problems.
Disconnect fuse is popped.
Wiring is wrong going to the heating board.
No wires for AC going to the thermostat

you have a short in the wireing.disconnect at air handler and hook-up short t-stat wire to t-stat,ifok chk wire to condenser

Hi!!! Does your ac unit work fine?If not check your low voltage problem..You have a low voltage problem check the wire going out to your condensor make sure that they are not touching..Good luck..Check low voltage wires..short in progress..

Your thermostat is calling for blower, your fan relay is stuck, or that model had a time delay blower solid state board on it which had the blower relay on it, and it could be bad. I would turn the power off to all of your system for a few minutes and see if this could make something happen.