A squealing heater is more than likely a fan belt. It may be loose, or it may be worn and need replaced.
check the wheel bearing
no u cant cause it might break the heater.
It might. Depending on the amount of blockage in the core. Don't apply too much pressure, you may cause a leak.
It will make your skin dry and might cause blistering or inflammation.
heater core could be rusty and old or line to heater core could be plogged most likely old heater core
it might
It sounds like it might be the switch or an overheated connector. Finding it might be difficult.
thermostat is stuck With my car, it was Heater matrix clogged with radiator sealant. The workshop cleaned it and it's start working fine!
It might cause the "check engine" light to come on.
If the engine is getting up to normal temp, the heater core might be plugged. Heater core is not plugged and normal operating temp!
Your heater core may be leaking, the condensate drain of the AC might be blocked, you can have a leak in one of the windows, or in the intake plenum to the ventilation .
I'd check the throttle cable or the kickdown cable. That squeal you heard in the engine compartment might have been a cable breaking.