Is AU aircon affected by thermo fans?

[ronwest]

The aircon (climate control) has been playing up lately.

Sometimes it's cold, sometimes it's not.

I took it to aircon guy this morning and he can't fault it.

What he did say is that if the low speed of the thermo fans only is working (ie no high speed) it would affect the aircon - build up of head pressure, (or words to that effect).

The car hasn't been getting hot - temp gauge sits where it always does.

So, any aircon guru's can confirm what he's saying?