About 2 years ago my car was blowing out cold air when I ran the heater I got the heater core replaced then it worked great. Last year I had the same problem I took it in they replaced the water pump and flushed it out. Iut worked great again. Now this year I have the same thing again. We changed the thermostat and flushed it again it worked great for a week and now its back to cold air. Is it the switch?