My heater is set to 90 degrees and its blowing cold air

You may have a clogged heater-core or low fluid levels in the radiator if one of the hoses going into the core is hot and the other is cold then it is most likely clogged undo both lines and facing the one down so not to get splatted with it use a hose and with minor pressure wash the gooey obstruction out until it runs clean and clear and flows free or you may also have a bad water pump open the radiator cap and with the car running look to see if its full and flowing and circulating if low add fluid if its not flowing i would say the water pump but give it enough time to exchange from the block to the radiator and if flowing replace cap or risk getting burnt ...also it could be the heat coils are not giving any help there should be a plug wire going into the unit near the fan /air-box remove the 2 screws and see it it turns red hot when switched on and also use a test light to ensure power is getting to it