I have a 1994 Honda Accord and we were in the Blue Ridge Mountains going up a steady incline. I had my A/C running and notice my car started slowing down. I turned my a/c off it gained some momentum.. Why?

 

Depends on a few factors.
How heavy of a load was on the engine?
I don't know the BRM range so I do not know what kind of elevation/grades there are.
If the grade is steep enough the demands of the A/C can greatly kill engine power. Gear ratios in the Accord trans can exacerbate the drop in power due to the 'tall' gearing.

If this is a 'new' problem verify compression, spark, fuel, air and general engine health.

 

In the SC/NC mountains anything more than a 6% grade is labeled on the interstates. My 94 EX slows and eventually drops into 3rd on these grades. But then so does my BMW and all of the cars I have rented. I will say that turning the AC off has never made much of a difference.

Now some of the hills between Cumberland, MD and Uniontown, PA make these hills look flat! The rental cars really struggle on them.

 

When you turn on the ac, it takes some horsepower from the engine because of the drive belt that's attached. It's completely normal.