A/C blows warm if it is hot outside and we are at a long light or in slow

Suspect insufficient air flow across A/C condenser... Possible cooling fan issue. .. At road speed, doesn't need cooling fan!! .. Also possible restricted A/C condenser cooling fins from debris. The added heat from either of these scenarios raises A/C compressor head pressure and cuts out compressor operation until pressure drops to an acceptable level again.

I had the same problem and it turned out to be the 2 cabin filters located under the passenger side kick cover(black). Air wasn't flowing thru.