Toyota Repair: 95 toyota 4x4 4 runner, radiator flush, heater hoses

Question
hi tim:
can you tell me why my 95 toyota 4 runner 4x4 heater blows cold air periodically ? when i start the vehicle it blows hot air for long time then only sometimes does it start to blow cold air suddenly . it does this sometimes so not every time we use it.and i have changed the thermostat and made no difference.what could be the problem? does it need a radiator flush or what? plz help

Answer
Mark,
Most likely is air in the system. Anytime coolant is too low or you change, when you add fluid the blower should be on high with the
vehicle idling so when the thermostat opens it sucks coolant into the
hoses and heater core. Check all hoses with your hand when its completely warmed up, they should be uniform in heat, if one is cold there is air trapped in there. (be very careful you don't get your hand near any belts or fan!!)
Normally over time if you have coolant in the overflow bottle it will
suck in more and eliminate air.
Next step is remove radiator cap when engine is cold, start up and run
until its warm and thermostat opens and it sucks coolant in, then
add coolant to radiator cap. Another way is slowly remove one of the
heater hoses while its warm and air will release.

Tim