My unit just started blowing cold air only when its on heat, what can i do??

SOURCE: my heat pump blows cold air for the first 10 minutes or so

Don't know how long you have had a heat pump but thats the nature of them in colder weather. Some people prefer to switch to "emergency heat" on the t-stat when temps fall below 20 or 25 degrees. This bypasses the heat pump and allows your back-up heat to heat the house. If your house is total electric your emergency heat is an electric furnace and it should handle the load if it was sized properly. Don't leave it on emergency when it warms up because your heat pump is much cheaper to operate than the furnace. As always, check your air filter since it can restrict the amount of air that moves thru the furnace, which is critical. Hope this helps

SOURCE: not blowing cold air

Your in house core could have frozen over. check the core inside the indoor blower unit. it may have frozen over. this will interrupt the cold air function.

SOURCE: window ac unit is not blowing cold air

When the unit is running, go outside and put your hand near the condenser fins, this air that comes out should be slightly warmer than the ambient temp. If it is not you will need to take the unit out of the window and out of its outer case and clean the condenser fins from the inside, this is no easy task as it is very hard to reach. You will want to get a small (toothbrushed sized) brass bristled brush with a long handle. Make sure the evaporator coil (in the front) recieves the same attention and wash the mesh filter that goes in front of the evaporator. Re- assemble and enjoy the cold air.