The heater in my 93 plymouth voyager is working proper yet blows cold air. why?

Start your vehicle and let it reach normal operating temperature. Then, look for heater hoses that run into firewall. Carefully, grab both hose, they should be warm/hot. If only one is hot,could be clogged heater core, T-stat could be bad or mechanical component that allows warm coolant to run thru, is not working properly.
When you change setting inside, your heater and A/C panel, from cold to hot setting, do you hear anything ? There's a flap that opens and closes the coolant passage. This can be a mechanical or electronic operated component.

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it will blow cold air until it reaches operating temperature dont understand what you want it to do it wont blow hot air right away notr made to do that

blend door is probably stuck, is the engine coming to normal operating temp?

this could be a hole in an AC line trace or have the lines traced replace and replaced Freon

So you are saying you'll have to find the source of the leak ?
The cooling fan would come on when the computer can't get a signal from the temp sensor. And the heater would blow cold if the coolant level was low.

I used to install AC in those, so I might be able to help. It is either the temp adjustment linkage, or it is the accessory selector. When you go from AC to heater does the air move from the vents to blowing on the floor? If so then it is possible that the linkage to the temp controller has probably slipped off one of the levers that controls the incoming air, from cold to hot. It is an easy fix. It would have to be that, because if you couldn't switch from AC to heat, you can always make the AC hot with the temp control lever.

need more info? Heater blowing cold air? Heater not blowing at all? If neither heat or air are blowing then it's just the blower fan. Easy to replace and fairly cheap.

could be a cracked block engine.what i would do is put a tarp or old sheet down park vehicle on it and wait then when you check you can look on old sheet to see where its leaking and it will give you an idea where to look for the leek if it was head gasket youd have sludgey looking whitesh foam in the oil

Check operation of heater coolant control valve, and it's associated remote control mechanism.
Check that both inlet and return heater hose is equally warm, as this indicates coolant flow through the heater core.
If no coolant flow:-
Check cooling system is correctly filled, taking care to bleed off any air locks from the system as necessary (with heater coolant valve open);
Check heater core is not blocked.