Why would my heat blow cold air

First, if you've recently changed cooling system components, it's really important to verify that you have purged all air from the cooling system lines. When you don't get the heat you're expecting inside the vehicle, the probable cause comes from one of two possible areas: 1 - The engine temperature is not getting hot enough. This can be due to a thermostat that is sticking open for too long. Testing of engine performance using a suitable diagnostic tool that will measure engine temperature is needed. 2 - Climate control concerns inside the vehicle are present. If you have a climate control concern, you can request heat, but the mechanisms that blend hot and cold air may not be working properly. This could mean that you don't get the heat you're asking for. Testing will need to be performed inside the vehicle with the climate control system to see what is going on. www.repairpal.com/repair-shops