About a month ago I replaced the blend door motor in the glove box that was clicking. It's starting to get Dewey in the morning this week and I noticed when I tried to use my defrost it only blew cold air. Checked my coolant level and it's right at the cold fill line and my operating temp is always right in the middle so no overheating. Sometimes it worked and others it didn't and just blew cold air, AC gets ice cold too! So it switches vents fine and I can control high or low but it stays cold. I recently started taking the reservoir cap off and starting it while squeezing the 2 hoses a few times. Not that I've been in there at all so I wasn't worried about air getting in but I wanted to try everything. I noticed this made my heat kick on about 50% of the time and stay on. I haven't gotten my coolant flush done yet so I did this morning and while they were burping it at the end my heat came on again. Problem solve I thought! Now it isn't working again and I can use some ideas from people in the know. I'd put my mechanical abilities at about a 3/10 and I've done the passenger side blend door motor, brakes and rotors and even did my 2 wheel speed sensor harnesses by myself so I'm not afraid to try to repair it but I'm at a loss with the diagnosis. Any suggestions would be appreciated as fall is coming fast and I don't wanna freeze here in the Midwest.