As the title says --

The plastic diverter is broken in my front trunk HVAC (well i guess it's just HV...) flapper valve on the driver's side, so when i have the heat on, i can't control the flow direction.

I have a replacement with an intact diverter. I'm going to install this wknd.

Any tips?

the paper tubes are delicate so use caution on them, brittle!!!! the flaps may benifit from a new seal material, I have used both foam neoprene and solid neoprene with good results, avoid cheap packing foam here you want it to last, so neoprene shoudl last long.

have fun