Where is located under hood the heater core valve??

Sounds like ur thermostat may be stuck open. If this happends the cars coolant system can not heat up to thr proper temp, which will give u luke warm air. I would start there. Does ur temp gauge operate in the normal range, or below , if it is below the range then thats the issue

Dear Jwhalen70 The heater always blows lukewarm air (not hot) and doesn’t mutter after how much driving, however it blows not hot…. So knowing this let’s exclude about thermostat, coz if it were because of “opened stuck thermostat” so after driving so much it would willy-nilly blow hot air.

see your other post Artur

where is the rear window defroster relay location on a 94 toyota corolla?