Could be a bad thermostat.
engine not warm, low coolant, or stuck thermostat
check thermostat, might be stuck closed.
I would change the thermostat first. If that dont work change water pump
heat core. leak. thermostat. no antifreeze.
The heater valve could be failing to open for one reason or another.
Poor coolant circulation from a plugged up heater core. Try flushing the heater core and replacing the thermostat.
Possible causes are, low on coolant, thermostat stuck open, clogged heater core or vacuum scorce not getting to the heater control.
No, not if it's on a heat setting. Most home thermostats have a "Fan" setting that will blow cold air if the attic is cold.
Low on coolant. Stuck open thermostat. Poor circulation (plugged heater core).
Your thermostat is the likely culprit here it is probably stuck closed. Have it checked out.
Probably your thermostat
The heater might blow cold air in a 2000 Silverado because the thermostat is sticking and not changing from cold to heat. The thermostat is usually located in a hose that leads from the radiator to the motor.
Thermostat and/or heater core may be defective
Low on coolant, stuck open thermostat, plugged heater core, faulty temperature blend door,
Could be, low on coolant, stuck open thermostat, plugged heater core, faulty temp blend door actuator,
Your thermostat is most likely bad. It controls the flow of warm water into your heater core which warms your air. Its a common problem in winter and an easy fix.
Most likely cause is a failed engine thermostat.
Low on coolant. Stuck open thermostat. Plugged heater core. Faulty temp blend door.
Thermostat stuck open. Heater core clogged. Heater temperture control valve defective. Low on coolant.
It doesn't really blow it out it just warms the cold air.
Low coolant? Bad thermostat? Heater control cable not adjusted properly? Heater core airbound? Heater core plugged?
Plugged heater core. Faulty temp blend door mechanism.
Poor circulation due to a faulty thermostat or a plugged heater core. Be sure the coolant reservoir is not empty.