cold or hot air inside

Lo is going to be cold
16C is still pretty cold (60F)
20C would still be colder than out side in my part of the world (68F)

I would guess at 23C, some small amount of hot air would trickle out for you.(72F)

 

I'm not sure I understand what you are asking. Are you getting no heat into the interior of your car regardless of your settings?

 

If temperature outside is 0c and it is not warmed up yet then setting the inside temperature to 16c, 20c, or HI will all just blow as hot as it can. So if I understand you correctly it’s working fine. If it still does this after something like 10km drive then maybe you have bad thermostat.

It is 0c here also. And in these temperatures it already takes time for engine and car to warm up.

 

I would start by checking the coolant level in your radiator. A low coolant level can prevent hot water from reaching the heater core. It is also possible that there is air in the system that might need to be bled out. The procedure is outlined in this thread: https://priuschat.com/threads/generation-3-coolant-change.142834/#post-2035121

If the coolant level is ok, you might need to replace the thermostat.

 

So even up around 25C and higher, it's cold? After driving the car a good distance?

If so, something is wrong. It could be a defect in the vent system electronic control. Or the engine-warmed coolant is not flowing to the small radiator in the ventilation system. Or it could also be a symptom that the coolant thermostat in the engine is failing, in the open position, allowing coolant to flow into the main radiator (in the front of car) too freely. The latter would effect drivability as well, the car wouldn't warm up properly, especially in sustained highway driving.

A mechanic would need to troubleshoot, figure out if it's one of the above, or other cause.

 

What do you have? ScanGuageII is one device that can read coolant temp. Fully warmed up engine should read 90~95C. Around town at lower speeds, with more electric driving, especially in winter, I'll see temps peak around 70C.

Coolant thermostats can go bad: they'll start to open too soon, stay open too late, and the rubber sealing gasket can harden and start breaking. All of this will allow coolant to flow into the radiator too soon and too freely, leading to overcooling.

 

3km in 10min at 3c? 58c might be just normal then. Did you test the heating system at the end of that trip? Still no difference between 16c and HI?

Try to make something like 10km trip? What does the coolant temp reach then?

This has info on how to change the thermostat How to replace engine coolant pump and thermostat | PriusChat filling the coolant is a bit easier if you don’t have the north American model with coolant thermos.

 

You'd have to google second gen, I don't have info. Try terms like:

Toyota techinfo prius thermostat 2006

One thought, if there's enough suspicion there's a thermostat problem, and you're comfortable with doing the swap, and a replacement thermostat is not too costly: purchase the replacement (and possibly replacement gasket?), remove the old one, inspect the gasket condition on both, and also:

suspend both in a pot of water on stove, with a thermometer capable of going to boiling point, gradually raise the temperature, and watch the performance of old vs new.

Regardless of the outcome, it'd likely be best to just put in the new one, due to the gasket getting hard/brittle over time. But it's interesting to see the differences. Use the new thermostat as a "known good" base point.

A thermostat starting to fail, in the direction of overly cooling, would tend to open too soon as temperature rise, close too late, and never properly close.

 

I think you should take a much longer drive before you decide there is something wrong with the cabin heater, like a 30 km journey.

3 km = 2 miles. If you drive such a short distance over 10 minutes, don't expect the engine to heat up. The Prius is supposed to be energy-efficient and the engine is not going to produce much excess heat given the very cold ambient air temperature and the short trip.

 

If that’s the maximum that it went to during the whole trip it sounds a bit cold. If that’s just something that you noticed during the trip then it sounds normal. How long did it take for the engine to reach those temperatures?

Thermostat starts to open 82c and is fully opened at 92c but thermostat is at colder part of the engine than the temp sensor.

 

That seems normal to me, especially with cool weather, around 5C. Likely your coolant thermostat is still fine.

 

Yup, it's fine. I had a ScanGauge hooked up, till about 6 months back, and in winter months it was rare to see coolant above 80C. Going up a local ski mountain is the one time it'd get right up there, to 90~95C.

Doesn't help your original problem, but good to eliminate variables.

 

After engine had warmed up did it still have the original problem? 16c, 20c, and HI still blowing the same temperature?

 

I'm looking through the trouble shooting section, of third gen repair manual. Unfortunately uses Techstream a lot, checking for codes. In lieu of that, maybe you can just check some usual suspects? A snapshot:



Here's something on that PTC heater, in a 2004:

PTC HTR ? | PriusChat

I wonder if you look in the engine bay, see where the coolant hoses run through the firewall to the heater, is the valve that controls flow in the engine bay? if so feel the hoses right at the firewall (with the heater set on high temp), are the hoses hot there?