HVAC problem We have a bryant indoor hvac unit. The inside fan motor comes on in heat mode, but not in ac mode or in the 'on' position. The thermostat, fan relay and motor have been replaced. Can u help?

Question edited to add MAKER.

Videos
https://www.google.com/search?q=a-vmh18sc-1+replace+start+capacitor

Part 8. It is held under a clip. When the image opens, rotate it to see the location and it is showing side-on..
REPLACEMENT PARTS LIST
..
https://www.appliancefactoryparts.com > 266743-1
PDF
A-VMH18SC-1. Indoor Evaporator. Page 2. Ductless Mini-Splits.


REPLACEMENT PARTS LIST. Heat Controller, Inc. 1. EXPLODED VIEW ...
Fan motor capacitor. 1.

no maker or model of HVAC told ,so the question is near impossible.
on my HVAC all fans have start capacitors that love to fail every 10 years. Others last 3 years max in the outdoor pad.
the fan can fail for dead,good or weak for sure and can be intermittent even work on cooler days. possible.
there are 2 things here, fan and cooling and they are not the same.
the inside indoor fan fails. and does not blow?
try to be learn model HVAC it is, and what works and does not work
both, tell both. air and cooling,
the AC side will ICE up if the fan fails at the evaporator coil and the controller detects that and shuts the cooling down, as ICE can damage it.

why not call for service as 99.% do now. just call the service, person. hvac.

a capacitor to a motor, outdoor unit has two motors, a fan and compressor motors. Indoor unit has a fan motor and a capacitor for it. Check the wiring diagrams.
Coil heats up? meaning contactor solenoid coil gets power? or, compressor starts up and radiator coil temp. heats up?
of the three motors, two outside and one inside, does one motor not work? if so, will need to check for power at motor leads and capacitor

There is a little motor on the heater box under the dash that needs to be replaced. It's called a blend door actuator...

According to my favorite HVAC buddy:

If your indoor fan isn't working it could be several things. Here are a few things to check before calling for service.
First make sure there is power to the indoor unit and that a switch or breaker isn't off. Then make sure your air filter isn't blocked. Sometimes that is the only problem. Some customers don't even know they have an air filter and it has never been checked. It can have a trash bag sucked up against it, or simply be clogged and dirty.Try setting the thermostat fan switch to the "on" position. Feel for air coming out of the vents.
If it is in the air conditioning mode, check for ice around the evaporator coil and refrigerant lines at the indoor unit. If the coil froze, the fan could be working but the air wont go through the ice until it melts. If the fan isn't working, that can cause the coil to freeze. If the coil is frozen, shut off the air conditioning immediately.
Some equipment still uses belt driven motors. Mostly furnaces only, not heat pumps. Sometimes the belts wear out, crack, and eventually break. If you take a look at the blower section of your heating system it is quite easy to see if you have a belt driven blower motor. You will see a motor sitting on top or next to a larger blower wheel connected by a fan belt.
Most fans are energized by a fan relay. This is probably the most common cause. The contacts inside the relay go bad. They usually stick open, never sending the signal to the motor. This is much easier and cheaper to repair than a motor going bad.
Of course, the motor can always go bad. Sometimes the bearings seize. Or the motor just burns up or weakens. Hope this helps.

Unless your compressor is burnt up, you probably don't need a new unit. If it's a 1998 it's not that old and you can get parts, the only thing is it's probably R-22 refrigerant and they must fix the leak in the unit if that's the problem before adding refrigerant and the refrigerant is expensive.. All they have in a heating and cooling system, that needs replaced, are a few parts. Outdoor unit has a fan motor,compressor, capacitors fan and compressor and a contactor. Furnace has a blower motor, capacitor, gas valve, fan and limit or furnace control board, which they still make replacement parts for.
My advice would be to call some more HVAC companies, till you find one, that is willing to fix your unit and not replace it..

Yes if your creful. There is a sequencer inthe unit that operates the fan in the heat mode. It sometime sticks. This is due the moisture from the ac sweating. You van pick upa sequencer at HVAC parts house. Just wire back wire to wire and you willbe ok. Kill power to furnace first. Rus

WAIT FOR DELAY

Check breaker for outside unit Also check to see if you ahve afloat switch on the inside air handler. Located under or in front of unit. It may be full of water and tripped. Blow out drain if tripped.

There should be 2 hot wires and a ground wire coming into the air handler. 120 volts on each wire totalling 220/240 volts across the 2 hot wires.
The 2 wires should go to a terminal block where the power is then distributed to the fan motor and heater coil.
If you have 15 KW heat coils or higher, you should have 4 hot wires and 2 ground wires.
The additional 2 hot wires would go directly to a heater relay.
If you can set your indoor fan for ON position and the fan comes on the outside unit is capable of getting low voltage power from the thermostat to come on. In which case you would have to verify both low voltage and high voltage at the outside condenser unit.
If you have no functions at all the wire you found loose must be reconnected.
If the technician is hooking and unhooking this wire between seasons you have a board or relay problem that must be addressed.
The entire system should operate correctly with all wiring attached at all times.
What is the model number of the outside unit?