Hey everyone, I just bought a 14 Prius and I’ve got a couple of heat issues. The first problem is the car won’t actually blow heat at all unless I lower the temperature all the way and then raise it. The fans will slowly speed up as the car warms up, but it will continue to blow ice cold until I lower the temperature and then raise it again. If the car has only been off for a short period of time, it will start blowing heat normally on its own, but if it’s been sitting there I have to do that each time I get in. The other issue is that it never actually gets very warm. It blows around 90° at idle and up to 110 when actually driving. I’ve had my mechanic do some work already. He replaced the thermostat which he thought was bad, and also replaced the coolant and bled the system. Neither of those seemed to make a difference. He did also run some water through the heater core, which seemed to help for a couple of hours, but ultimately went back to only being lukewarm. My mechanic wants to do an actual heater core flush with CLR and let it cycle for a couple hours, which makes sense, but I’m still wondering why I have to lower and raise the temperature to get the heat to actually come on. He seems to be completely stumped by that part. Just wondering if anyone else has had similar problems. Thanks for the help!
Sounds more like an ecu issue, but I have never read this particular issue before. Not sure how much money I’d be willing to throw at a mechanic who is guessing
It sounds worthwhile to monitor the position/movement of the blend door, either by watching its position on a scan tool, or poking your head down there and looking, or both. If hot air can be blown out sometimes, I don't think there's a blockage of coolant through the core.
Set your cabin temperature to max and kick your HVAC system to manual mode. If it works fine in manual mode, there's something going on in your cabin temperature sensor or HVAC ECU. Both can be monitored and verified with the proper scan tool.
