No heat when i turn on the heater on 1998 camry

here are the steps in the correct order (works on all cars)
they all work the same, but controls vary.
eg: liquid to air heat exchangers. all.

http://www.fixkick.com/AirCond/heater.html

Don't replace it until you have checked it out. It might be a bad heat valve on the heater hose, the control to the valve may not be opening/closing it, there might be air in the hoses, the antifreeze level may be to low to supply the core...

Sounds like your heater core went out or is plugged, try doing a coolent flush on your system and if that dont work then youll propably have to replace the heater core. Hope this helps

could be your temp control actuator which is under the dash

Camrys are picky when it comes to a properly functioning engine thermostat. If this is stuck open some, not only will you get little heat, your engine will get all gunked up with varnish. This is the first thing I would check. (Read the engine gauge - if it comes up to temp after no more than 5 minutes of driving, then it should be good.) If it is not this, try cleaning your coolant system, making sure the heat setting is full on while doing the cleaning procedure. (Prestone makes this product.)

We are sorry to advise you that the 1998 Camry product does not have a cabin air filter.

This feature was released starting with the 2004 models

First of all, check coolant level, and when adding (if necessary to add) turn heater on while topping it up. Then start investigating why coolant was low.
Let me know what you find as far as level goes.

The heater may not work because of a bad thermostat, low coolant, or a bad sensor at the engine. It can also be a bad resistor valve under the dash. The resistor valve is connected to a wire plug on the blower motor under the dashboard. It needs to be replaced. Th AC may need to be refilled with refrigerant or the compressor may be bad.

was it over heated? may need to check for blown headgasket or leaking water pump

check the heater control valve. its a plastic valve in the engine compartment, ensure the cable is attached and also ensure that the valve moves when heat is selected. also it is possible that someone has bypassed the heater core due to a leak. check to make sure both hoses are still connected.