That will be interesting to hear your view of the heater.
R704 the fan has only two speeds, speed one is just moving air, speed two would be a fair and decent speed, My Perentie defrosts the windscreen on negative 5-6 degrees from cold start just idling in 10-15 minutes, when driving from cold under 10 minutes.
Are you getting both speeds?
Just a question to both, how good and effiecient is the cooling system, if the cooling system is performing poor the heater will be worse.