No Hot Air at Temperatures Below -5

[excash]

I have a problem with this GLE 43 W166 2018.
When the temperature is below 0, there is no hot air, when 0 and above, everything is fine.
The fan works, and I changed the thermostat.
Any suggestions would be helpful.

 

[Mersovod]

Check all temperature sensor values for adequacy in Xentry.

 

[tsulovari]

As Mersovod said, check the heater core temperature sensor. You may have a clogged heater core. I just did the same thing with a GL550 X166. I flushed the heater core and after that the heat was normal. When the outside temperature is too low, the heater core flow is not enough to heat the vehicle.

 

[Aleks991]

If you bought a thermostat that opens earlier, for example at 75 degrees Celsius, then this will happen because the engine takes a long time to warm up in winter, especially at temperatures below zero. It is possible that the system was not flushed and blown out correctly.

 

[excash]

The customer took the car to the dealer and they said the problem was in the heater core. The customer doesn't want to do that.
Thanks to everyone who helped.