2006 Prius with no heat

Check your coolant in your radiator and in all the hoses coming to and from the radiator if this is a generation two I'll look at the tank right behind the radiator towards the engine there is a opaque whitish looking tank that should be filled up to the crosshairs on the bottom of it with coolant for this conversation anyway so now that it's not full to the cross in the bottom of the filler neck take some Asian red coolant and pour it in that hole until it gets to the cross at the bottom of the filler neck. Now if you will squeeze on some of the fat hoses that go from the radiator to the engine restart the car go for a drive and see if you have heat If this doesn't work you may need to check the three-way valve usually that'll be clicking and making noise under the hood more so than the inverter pump when it's not functioning correctly.

 

Scroll down to the "codes from the heat/air conditioning system" on this page, and let us know of any codes displayed.

Blink (a/k/a Flash) Codes – How to. | PriusChat

 

How long were you driving before the problem showed up? When it's that cold out you need to be driving for more than 20 minutes to be sure you have the heater system via the engine coolant. Before that time its mostly the heating element and you can check that fuse.

So you have two systems and which one is the problem is defined by how long you've been driving... If its an engine coolant problem then your thermostat in the radiator could be stuck closed (leads to engine overheating) or the valves that sends hot coolant to heater core is not working, but it's likely the heating element would still keep working. OR maybe both systems have failed? Or maybe your buttons a glitching out, in which case you may be able to fix it by disconnecting the 12v for a few minutes, which resets/reboots all the computers.

Also, essential to HVAC diagnosis is removing or replacing cabin air filter.

 

Just top it off... My understanding is that part of the system only needs bleeding when you replace the pump. But if you want to hook a hose up to the bleed valve/nipple about a foot in front of the reservoir with other end of hose in reservoir you can un screw the nipple and watch the coolant travel through the hose to confirm there's no air.

 

The fluid in the inverter loop isn't going to evaporate, nor can it go out the exhaust like the coolant in the ICE loop. If it is low there is a leak some place. Best find it now. With luck it will just be a cracked hose. If it has been coming out fairly slowly there will probably be a pile of pink crystals at the exit point. (These might also be present at the bleed valve and not be a leak. If the clean up after the last time it was bled wasn't thorough a few drops spilled near there will have crystallized.) A mirror and a flashlight will help as there isn't a lot of empty space where those hoses run.

Another possibility is that the relevant vent door mechanism failed and it shifted to block the hot air. That should show up as a trouble code (with the right reader) I believe.

If you didn't hear gurgling at any point it probably isn't the heater core.

 

The inverter coolant loop is entirely separate from the engine/heater/thermos cooling loop. That said, they should both be filled properly.

 

Check the heater fuse... When engine is cold an electric heating element warms the cabin... Of course if you still don't have heat after driving more than a 1/2 hour it's more than the fuse.

 

The electric heating element while the engine is cold provides a slightly useful amount of heat (about 700 watts) but not really enough to feel (for comparison, you get about 5300 watts of heat from the coolant once the engine's warm; that's what "having heat" feels like).

About the only way I've ever been able to tell any difference between the electric element on or off is defogging the windshield of a cold car. The air really won't feel noticeably warmer, but the fog goes away faster with the electric element on.