There could be several causes of this. The air blend door may be stuck, preventing it from channeling only hot air to the inside. You could have air trapped in the cooling system.
If the temperature gauge is reading below normal operating temp after driving a little while it may be that your thermostat is stuck open. I replaced my thermostat and it fixed mine.
It could possibly be a clogged heater core
I have 95 cavbalier new heater cor new thermostat puts out very little heat any suggestions
Thermostat stuck open, heater core clogged, or the heater temperture control vlalve is defective.
It's in the thermostat housing between the actual thermostat and heater hose. Has a little insulated wire coming out of it.
Thermostat stuck open, clogged heater core, heater flow valve not functioning, or low of coolant.
It will take a little longer for the cooling system thermostat to open up if the heater fan is on. The heater fan and heater core act like a small radiator and disperses heat energy when in operation.
Some advantages of using a base board heater are: requires very little space for installation, the system is quiet, requires very little maintenance, it is safe to use, and allows the owners to control it using the thermostat.
If you're talking about an automotive thermostat and an automotive heater , then you should go with whatever temperature range thermostat the manufacturer originally specified . If you live in an unusually cold climate , you can go up a little on the thermostat heat range during the cold weather .
The heater door control on a Blazer can be replaced by purchasing a new one. The heater vent will pop out with a little nudge from a flat tipped screw driver. Then insert the new heater vent door control.
Did you check the thermostat? If so, try the heater core. check the air mix door in the heater it may be stuck and letting outside air in
Sounds like a heater hose got left loose or maybe one of the hoses are leaking a little.