2004 6.0 176,000 miles

A/C started blowing hot sometimes...mostly when sitting at a light, but sometimes while running down the freeway. The condensor is clean, and the fan works.

It will blow hot for a while, and then start blowing cold.

When checked with guages, the pressures where in line.

I was told it could be a blockage, or a bad pressure switch.

Where are the two pressure switches located?

Has anyone had the same problem, and what was the fix?