How do I fix the problem my Espar heater under the bunk

White smoke is probably steam which means you have either cracked the block somewhere or blown the head gasket. What are the symptoms of Blown Head Gasket BlueDevil Products

Head Gasket --if white smoke comes out the exhaust

If it overheated (one time) -- you would stop using it,would you not ?

No---------- then you ruin the motor----- but you know that

With or without the motor running? See if there is a difference.

The white smoke is probably steam caused by coolant getting into the cylinder(s) either from a faulty head gasket, cracked cylinder head or cracked engine block. The loss of heat from the heater indicated that coolant was being lost..

coolant leaking into engine probably blown head gaskets. More damage will occur the more you drive it. Unfortunate and expensive repair on a northstar.

Your heater core is shot. Coolant leaking on the floor (wet) and driping onto exhaust (smoke).
Replacement of the heater core is the only proper fix. As a temporary measure , you could disconnect the hoses that run to it , and plug them (or join them together). Engine will run , but you will have NO heat in car. enough of your coolant has probably leaked out to cause engine problems. Make sure it is refilled and air removed from system before driving.

yes and could be caused by a stoped up heater core or runing it hot

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.

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.

if the car is not overheating, the thermostat is working fine.... replace or flush the heater core multiple times to try and eliminate sediment build-up.

the heater doesn,t work blows cold air