# 1 .. it is hardly ever the ECU ,, so i would skip that idea for now ,,

but it could be

a/c clutch GAP too wide .. if it is too wide the coil does not have enough strength to engage the clutch especially when really hot outside .

could be as advised a intermittent failing compressor clutch relay , i have seen it many times

and also as advice it could be the thermostatic switch ,, located in the evaporator

BUT it could also be a # of other things ,,poor connection , high pressure switch, internal fan switch ,it provides the ground path for a/c system etc..etc..

In other words when a/c is inop you need to properly diagnose it before you start replacing parts