Firstly its basic function is to supply 12 volts to pin 1 on the webasto heater, nothing more nothing less.... however the reason it costs so much is the range of the unit .. its huge...
the timer function ( how long you set the heating for is all built into the remote) i.e. you can set one remote for 20 minutes and another can be 40 .. its all done in the remote not the receiver itself i guess it sends a different code to how long the heater is required..
Anyway... basically the telestart sends 12 volts to pin 1 on the heater, this then wakes the heater up and starts the burn cycle... warming up the engine block and the interior.
the interior fans will come on approx 5 minutes after the heater is started( it does this bit by sending a data signal from the webasto to the cars heater / aircon module.. i think its a can bus signal - this bit is installed already in the heater) this ensures that there is sufficient warmth in the engine coolant to heat the interior.. the vents will automatically allow warmed fresh air in and points the vents up to the windscreen to defrost it and also down the floor to heat the cabin.. this is not changeable... this will mean you will never have to scrape ice from your car again !!!!
The heater will shut down in the following options....
you press the button and it turns off
you get in the car and you drive off - the heater will self shut down and the timer will disable itself.
the cars battery get to low ( this is to protect the car) it enables you to still crank the engine to get it started !! cool!!
the coolant is already too hot..
its way to warm outside to be using the heater anyways!!
Note its a good idea to run the heater in the summer to keep things from seizing up or going faulty !!
You can also wire up the telestart to work in summer mode... by adding another wire to pin 5 (i think) from the telestart as well as the pin 1... you then use the remote to select summer or winter mode by pressing a configuration of buttons.. NOTE i did not install this feature on mine as it basically blows the outside air into the car. (no air conditioning) i found that simply using the BMW remote to open all the windows before you get into the car does exactly the same ting a lot quicker
The different models are explained below:-
T70 a basic kit with just activates the the unit depending how long you set it for.
t80 this unit unit will send conformation that the telestart has received the transmission by giving you a conformation light on the remote !!!!
t91 exactly the same as the t80 but the remote is much much smaller ( you can use a t91 with a t80 receiver if you already have a t80 kit
t100 this one does all the above.. but also alows you to set the time you intend to get into the car from the remote.. so you can set it the night before and as long as the unit is in range it will start the heater for you at the required time..
If the car is already warm and say you come to a level crossing .. you can turn off your engine and use your rest button (max button on later cars ) to keep the cabin warm.. if the cabin starts to get cold the webasto will automatically fire up again keeping the car warm!!!! (all diesels do this regardless weather or not telestart is fitted) without the need to start the engine!!!