AC started blowing hot air. Clutch is not engaging

From past few weeks AC started acting wierd. It used to run find in mornings but as the day got hotter or if I put vehicle in sun the AC used to switch cool air to hot air once in a while.

From yesterday it is only blowing hot air. I showed it to a mechanic and he says there is a voltage but thinks the clutch coil is the problem. Asking around $600 to change it.

Just want to be sure it is not a simple relay problem or Freon pressure. Repairshop couldnt find out the pressure as clutch is not engaging. Can I short it and measure the pressure? If so how could I do it? Also how to check whether it is a relay problem (I was reading lot of online forums and MDX has relay problems for this year range)