1995 volkswagen Jetta, when I turn on the defroster on steam comes pouring out.What should I do ?

If there is a foul ordor coming from the vents (smells like old antifreeze), then it's probably caused by a leaking heater core. You would also have to add coolant from time to time (depending on how bad the leak is). There might be coolant leaking on the carpet of the passenger side floor, near the firewall.

Another possibility is that the evaporator (a part of the A/C system) is freezing and the vapors you see are from the ice which accumulates on the evaporator (this can be cause be a bad expansion valve or orfice tube).

** the a/c compressor turns on when you turn on the defrost.

It is always important to know that foul odor is a sign that can cause the heater core from leaking. This is what we call for the safety and prevention. In connection to such issue about prevention and safety measures, CNN Money reports that a wiring problem in newer Volkswagen Jetta sedans built for the United States industry between March 2010 and March 2011 may cause the auto to shut off if the horn is used. To date, no accidents or injuries linked to the wiring problem have surfaced, however the automaker is erring on the side of caution. Do not take out a cash loans for that new automotive just yet.

I agree with bfree.

for info on replacing the heater core:

http://wiki.answers.com/Q/How_can_you_replace_the_heater_core_on_a_97_VW_Jetta

It's pretty involved so you may want to consult a shop for prices; if the instructions at the above site seem a bit much.

other than removing the dash componets, it's realy not too bad, if needed i can send you the info and some tips on removing it, let me know.

Let us know how the repair is going.