I have discovered that in the cold days if I select HI temperature setting, the inside air will get hot, even when the engine is cold. If I keep the temp setting normal (24~28 C⁰) the car waits for the engine to open the big circuit of water cooling to start the fan for inside ventilation and then the air blown is warm. I want to ask someone who knows, if the car has electric resistive heating, or if it uses the compressor from the AC, in reverse, like modern AC units, to heat up the cabin. I own a 2021 Octavia 4, with 1.0 tsi engine, manual transmission and ambition trim.

With the thermostat and the valve to the heater matrix closed, the coolant gets warm very quickly. Normally, the car gets the engine up to temp as quickly as possible before opening the thermostat or heater matrix valve, as you have noticed. It's not the relatively small amount of coolant that's 'warming up', it's the massive stone cold block of aluminium full of oil.

 

I think you are just bypassing this and opening the heater matrix valve early by setting the AC to 'high'. A up to temp car has a coolant temp around 100 deg C, but you can comfortably warm the cabin with the coolant of a engine that's warming up.  

 

I doubt there is a resistive element or that the AC is running as a heat pump.

 

My friends old Cavalier could boil your face off 2 minutes after you started it, it was quite impressive.

Edited 30 December, 20241 yr by baka

Some models do come with a PTC heater element as standard, although I think they could be mostly diesels. Can you look at the option codes your car has to find out?

 

A previous Jaguar I owned had a 1kw PTC element in the vent system and that defrosted the screen and started to warm the interior within seconds of a cold start.

In the hybrid you notice the battery range dropping while you're warming the car up.

The IV hybrid has got an aux heater in for warming car when starting on battery or preheating from phone