Bmw 530d taking a long time to cool First time this has happened after major service Vents giving hot air on cool setting Temp guage shows normal

I am not to sure what u are asking here but I would say u need 2 glow plugs . I would be checking the dpf filter as that gives off a light colour smoke when trying to regen and if it can't regen that is where the fuel is getting in oil , modern diesels need to have long runs quite oftern driving around town blocks up dpf in the exhaust the car try's to regen using extra fuel to get it up to temp to burn off the soot inside it prob not running long enough to do it. If u got good diagnostic gear u can preform a regen stationary hope this helps

is the cooling fan cutting in ? run the engine whilst stationary with the hood up , give it a little gas 2000revs and wait for the temp gauge to rise ,the cooling fan should be heard cutting in , and off again once cooled the engine temp down ,this may take 10-15 mins but you have to be sure the fan is cutting in or you may cook the engine

I would also pull the thermostat and check it for closed and correct operating temperature range.

1st check fuse to the heater
2nd check relay
3rd the filament wire of the heater

The head gaskets blown

Sounds like the Coolant is not full and has a air bubble. It is very important to have the system filled complete. That would be the first step.Good luck and have a great day.

It sounds like the control motor switching from hot to cold is stuck halfway in between the two temp settings. You will have to take it down and replace it, it is mounted under dash passenger side near the blower motor.

the climate unit has an internal fault

An overheating engine will often shudder and make a unique popping/rattling noise. Is it doing that? If it ever does that it's time to call a tow truck or further risk major engine repairs.
Try turning on your heater. Your heater makes its heat by blowing air through a mini-radiator (like the one at the front of your car) and pushing that hot air through to the inside of the car. Is the air coming out of the vents warm to normally hot or I-just-opened-the-oven make your skin tingle hot? Check and make sure you have coolant (when the engine is cool) and fill to where it should be. There may not be enough to circulate through the cooling system but enough to hit the temp. sensor and give you warnings.

You may have an air pocket in your system which some times happens.  One way to get rid of it is to take the upper hose off on the engine side,  fill your system with water until it runs out from your engine block, replace the hose, start your car turn you heater on and set to hi keep the radiator cap loose until the temp start to rise then close tight.  Once the air pocket had been remover you can drain some of the water from the radiator using the lower drain plug and add antifreeze.