You have probably blown a major fuse in the under hood fuse box. You need to find the cause of the short.
does fan door motorized or on a vaccuum line when you switch from AC to defrost?
either the fuse that was put has too much wattage or not enough
That means either you have air in your heater core or your heater core is being bypassed
When there is a problem in the vent system it defaults to defrost setting. Check the doors & vac supply
Might need more coolant or may need to replace thermostat.
The AC on a 1998 Dodge Ram 1998 will only be blowing out the defrost vent if the air handler is not set properly. This can result from a piece of debris getting stuck or a faulty flap.
you have a vac. leake or the oneway check valve is not working.....
If you feel no air blowing at all (when you are not moving) then your fan is not blowing. If it is blowing air, and it is cold, when the heater is on, then most probably your heater core is leaking, or is clogged. These are easily replaceable and go bad all the time in older cars.
You have a vacuum leak causing your vents to switch from dash to defrost.
The rear window has probably been replaced at some point with one that has defrost. The rear window has probably been replaced at some point with one that has defrost.
It is something you can do, so it is a verb.
If central air conditioner turns on but is not blowing through the vents, check the filter. If it is dirty, change it. Change the thermostat into cool, this will defrost the air conditioner.