usually it is a vacuumn problem right at the heater control switch or sometime under the hood
Low coolant? Wrong thermostat temperature range? Heater core plugged,restricted or airbound? Water pump not circulating coolant? Temperature control cable not adjusted properly?
you must be a wierdo.stupid.
When my heater didn't work i had to replace my thermostat.
I have a 2000 zx2 and it has a thermostat, if that is your question. Having said that, my heater quit working and it turned out to be the cable came loose under the dash on the left side of the radio. At first I thought it was the thermostat but was wrong. Duct taped the cable in place and the control and heater started working fine again.
Try taking the car in for a rad flush. You may have a restriction. Check also that the hoses are not kinked, block heater and rad.
Wrong thermostat? Wrong installation procedure?
Probably your thermostat
could be thermostat or heater fan if you can hear all the speeds on the blower motor working then it could be your thermostat but your heater core might be plugged as well
check your thermostat or your heater core may be getting ready to go out
I would guess the thermostat I would guess the thermostat
Usually a thermostat will fix it, could be low coolant, heater control, wrong thermostat (should be a 195 degree) or restriction in the heater core or cooling system also.
air block in heater hose most likely bleed it