Defrost not working well, amount of air blowing is low. Acts like a blockage problem, all other parts of the heater system works fine.

Sounds to me that you might have a leak in the line. Those heaters are all Vacume actuated.

Mode door actuator . A electric motor that controls a door that directs air flow .

First things first.....You must have the air conditioning system hooked up to an a/c system machine and then checked for leaks and also read low and high side pressures. If there are leaks then low Freon (R134a) content and low refrigerant oil can cause the a/c system to not engage the a/c compressor which basically means you will not have proper defrost functionality nor regular air conditioning. Most shops, when working with your air conditioning, will install air conditioning dye to assist them in locating leaks and is the first step in diagnosing all a/c systems. Post the findings after thw

it acts like it is low on coolant,or your heater core is partially stopped up.

The heater tap is not working, find it under the hood where the heater pipes go through the bulk head, If the tap works there is a blockage in the heater radiator or the tap is faulty or the controller inside the car is faulty.

Seems like the dampers are partically closed,look under steering column and see your duck work for the vent system.Follow it back to the blower box.Unhook if there, turn on ac, if you get full air, nice and cold on low and high you have blockage in your vent duct work,check the vent line that diverts air to the diffrent selected vents. Also check for vent disconnection around sterring column,and defrost vent area.

i believe this is a vacuum operated system. if there is a problem with the vacuum supply to the control unit, it will automatically default to defrost. i would start by checking the vacuum source lines. good luck!

Either a faulty thermostat or air in the system. Bleed the system and you still have no heater then get a new thermostat put in.

I would start by checking for coolant leaks. Common places would be in the waterpump or heater core. Heater cores can crack and leak. The heat from your vents inside the vehicle comes from air passing over the heater core, which is heated by the hot coolant flowing through the heater core. It acts in a similar fashion to your radiator, with the purpose of heat transfer. A coolant system that is low on coolant will not transfer heat through the heater core. Also, deposits from the coolant system can collect and plug the heater core which will restrict the flow and the amount of heat that is transfered to your heater. If you don't see coolant leaking externally, it may be leaking into the engine. this may be from a blown head gasket or warped head. If this is the case you may notice some whitish color smoke coming from the exhaust, as well as your coolant overflow/storage tank fluid level may increase.
The air conditioning is a seperate system and may be a seperate issue. The system contains liquid freon like a refrigerator. You can by recharge kits at your local autoparts store. If the kit works, you may find there is a leak in the system and you will loose cold air after some time. If thats the case, a certified dealer can fill the system with colored dye to help locate the leak. A bad compressor or evaporater can also cause a/c systems to fail.

Your system has R-134 Freon in it. the 134 is made up of smaller molecules than the old R-12. The R -134 permeates through the rubber parts of the system. If the system gets too low on Freon, the compressor will stop coming on.(low pressure cut out switch). Have the system serviced with an A.C. machine that can vacuum, measure the amount of Freon in the system, and add the right amount. The machine can also inject die. Later the die will show up under a black light.This will show any leaks you may have.