99 jeep grand cherokee, Defrost heater does not work, fan control in car does nothing and Ac also nothing

Check for melted wires or connector at the blower resistor. It's located near the blower motor which is under the dash above where the passenger's feet go.

JEEP WJ. 99
sure, most have a resistor block.
and all of them on all cars made with them, love to fail.
the fsm covers this, factory service manual.
or alldata.com
or free here.

item 12 here
see it?

http://www.factorychryslerparts.com/showAssembly.aspx?ukey_assembly=632719&ukey_make=1064&ukey_model=15529&modelYear=1999&ukey_driveLine=7406&searchString=blower

Usually a vac leak. I would check for a leak in the HVAC control system and the line thru the firewall to the engine.

Have a good mechanic to check to see if the door of the a/c and heater and defroster is working properly. I had the same problem and one mechanic said he could fix it for $750. I got it fixed by an honest mechanic for less than $100. Good Luck!!

Replace fan relay
$45 DIY
check out http://rigs.corequipment.com/cebby_WJsite/cooling.htm#relay

see if the air duct piping is still connected to the blower housing or the fan blade might have come loose from the motor and the shaft is just spinning inside the fan blade

replace the blower speed control resistor, they short and allow this to happen

Check the blower motor under the dash.(on right side put a 12v lead directly to the connection and if it works, the problem may be in the switch relay or resistor pack. (i've also heard of debris holding the fan from moving so if there is power there and motor does not run, remove & check first before buying a new unit.)

Alot of people have the same problem with the fan switch and blown bulbs. There really is no fix for this. Jeep really screwed up when designing the heater control assembly. The cheapest solution is to buy another unit off Ebay. Can always go to the dealer but be ready to PAY for there mistakes.