Hi everyone, this is my first post but I thought I should get this info out there.
I had similar issues with my 2005 Hilux. It hasn't got the factory cabin filter so debris over time clogs up the evaporator.
This lead to poor cooling and a weak blower fan discharge as the first symptom, then the dreaded aircon trips off on hot days.
I had bubble free fluid in the receiver drier window up until the aircon amplifier trips the power to the compressor clutch.
At that point I had no fluid in the window. (had gas checked and was confirmed ok)
This lead me to investigate further finding my Evaporator extremely clogged.
I removed:
1) Glove box (for access)
2) The blower fan. (simple to do and much needed clean required for me)
2) Partially removed the Blower housing (enough to see/reach the lower half of the evaporator)
(There is a spigot that the housing sits on and it needs to be lifted up off the spigot prior to lowering down)
Once access was gained I used a workshop vac and compressed air to clean the evaporator and enclosure in situ,
(surprisingly high amounts of gunk/leaf matter removed with roughly 80% blocked fins to start with)
I also blew out the drain line and all of the ducting as far as possible.
From there just restore the access gained and the results were fantastic.
Twice the airflow and much cooler flow.
(total time under 4 hours and could be quicker if you knew what you were doing)
Hope this helps people.....
