Pardon my ignorance, is it under the hood or under the dashboard?Sure. I meant drill a hole in the side of the HVAC unit, right alongside where the fan controller inserts. I would think that would allow the stuff to be sprayed into the airflow before it reaches the evaporator, preferably downstream of the heat diffuser vanes (so as not to contaminate them), with the controller in its fixed position. It might be possible to pull the controller out a bit to allow a gap to insert the tube alongside, but I believe the vanes get rather hot so might melt the tube.
ThanksDepends whether pre or post 2006 I think. The design of the HVAC peripheral bits and pieces evolved over the years. It will be behind the kick panel to the right of and higher than the driver's right toes, or on the symmetrical location in the passenger footwell. In either case the horizontal panel with the courtesy light has to come out from under the dash, and if it is passenger side, the glove box too.
Its a pain to access from the agility standpoint, and its easier if you remove the seat so you have more room to lie on your back. I'm skinny, and built a platform level with the door sill to half lie on, and didn't remove the seat. Alternately you could jack the side of the car up and kneel on the ground. Depends on agility.
The head of the controller is about the size of a credit card, might be behind a thin transparent plastic cover, and is held by two 6 mm screws (there are 4 holes but 2 are utilised).
View attachment 275146
This is the outside face, and it may not have the yellow sticker. Its nearly as big as a credit card. The radiating fins are other side, projecting into the air flow.
You may not be taking it out of course, if its possible to inject the gas beside it through a drilled hole (make it downstream).