Why is AC blowing cold air only in freeway or when is above 40mph?

May be low on refrigerant due to leaking parts or o-rings. May be condensor fan not blowing. This would affect idle & low speeds, but at high speeds would have enough air flow to scrub heat off condensor. This is definitely a problem for a shop since this a/c compressor system is labor intensive.

freon level or not enough air flowing over condensor at lower speeds

See if radiator fans are working when A/C is on...

Who and when was it properly evacuated , vacuumed down and recharged with R-134 & dye(to help locate leaks)? Also if engine is running hot the PCM may 'command' the A/C 'off' due to condition. Find out why engine is running hot , may solve both issues at once.

I have EXACTLY the same issues with my 1997 honda crv's a/c. It is impossible to think its a low freon, leak,etc. issue. This has got to be a faulty part like the compressor.