Heat working and stoping

i have a 91 toyota pickup and my heat will work sometimes but for the most part it barley blows out any heat it has a new rad and thermostat i dont no what else to try and fix it

Make sure any air in the system has been purged.

are you saying that it won’t blow? or that the fan blows plenty of air but the air it blows isn’t warm? if there is little air blowing at all then you have a problem with the blower and/or vents. other than that check for air as suggested above.

no i blowes air very good just dosent stay warm and i had the heater core checked today and thats fine

Maybe the heater core is clogged. Are both hoses hot?

thanxs everyone turns out my thermas was defected