I purchased a monovalve repair kit to replace the faulty unity with a torn rubber diaphragm. The new one I put in doesn't seem to work at all. All I get is cold air. I put the old one back in with no diaphragm on it and it delivers hot air full on. It only worked on low before that. What's going on? I have troubleshot this problem for days and all I have come up with is use the faulty monovalve for winter and the replacement for summer. I have already flushed the heater core, i have checked for blockages and the heat works perfectly with a modified unit with no rubber diaphragm but not with one that is brand new. Help!