Replaced heating core and now no heat

alot of times I found guys are pushing the buttons in an a/c car to hard and push the back away from the selector switch.. I have seen this on several cars that we worked on. Take the switch out and you will see the back push away when actuating it. If it does it is not nessarily shot. I have fixed many. Auto zone has a tw part glue for plastic only. drys in 5 min. While you are holding the back against spread the glue around the edge. once it is dry it should stay stable and be stronger then factory. This switch was used for several years up through the 90's and is a common proplem. It will only will be used on an A/C car . but sinse you mentioned vacuum I am assuming it is. Steve