I've read about plenty of similar situations, but I'm double checking.

I replaced the actuator, heat works, but still gets cool when blower is on high and/or when slowing down/idling. I'm assuming that the blend door itself is not working properly?

I can make due with the weird heat situation, but I'm thinking I won't be happy in the summer when I'm running the AC. How do I resolve this?

 

Did you confirm that both heater hoses are getting hot and staying hot, even when idling? If not, then i guess you know what you need to check.