If it does blow warm shortly, it could be low flow through the core either by a plugged core or restriction to it. If you can get to the connections and disconnect, you can try compressed air through it. Or if you can determine which line is outlet, disconnect it and when started, check the flow. Your heater control valve should have vacuum at the line when heat is requested.
Wednesday, October 14th, 2009 AT 11:21 PM