Just want to pick experts brains on air con system, Discovery II with the rear air con unit, now i am no expert on air cons coming from a cold climate and air con being an option. after fixing my compressor clutch thought good can finish it off and top up gas it held pressure for 2 weeks so had also fixed the very slow leak. but when the air con man connects gauges it is showing that there is a blockage and he was saying TX valve not working.

After driving home and having the rear unit turned on sort of thought would rear unit have a TX valve and yes it does after looking at workshop manual so what would the chances of them both failing?

Have heard that the receiver dryer can block up too and that is a lot easier to replace than TX valve on front unit, would this show same symptoms as faulty TX valve or in my case valves as i believe both would have to be faulty to show up as blocked, if I remove filter and cannot blow through it then it would be blocked, not sure if a new one can be blown through as never tried it.