a/c won't cool at idel

I have a 1999 2500 2wd suburban 7.4L....the a/c will only cool to a temp of 60 degrees F. at idel. It cools down to 54 degrees at highway speed. This only occurs when the outside air temp is above 90 degrees.
Under 90 degrees it cools fine and will freeze you out. I think that the aux fan on the front of the condensor isn't working...When is this fan suppose to run? Will this cause my problem? The r34a charge is within limits. It is a new fan and condensor last fall after a deer accident.
Thanks...

sounds like normal operation to me

Sounds fairly normal to me as well. It will always cool a bit more under highway speeds due to the fact that the condenser pump will be much more effecient. Keep in mind you are trying to cool a lot of interior space when it's hot outside. If all else fails run the beast down to Creston to the FORMER Cornick Chevrolet. Hopefully after the change of ownership and the loss of the outstanding service manager they can help you out.

You say the electric cooling fan doesn't work, it needs to.
On my 91 2500 two years ago, the AC didn't work at all during idleing like intown stop and go, but on the road you could hang meat in side it was so cold.
I found that my extra electric radiator was not working and the 7.4 was getting warmer than normal. Not much, just few degrees warmer and the compressor sensor would turn the compressor off. I found the electric fan wire at the engine has grounded out due to the insulation of the wire decay and repaired it and the electric fan started working again.
Then the AC keep working at idle again. I think the engine temp sensor was sensing the extra heat of the water temp and turning off the AC compressor to help the strain on the 7.4 at idle.
Fix the electric radiator fan not just for the AC, just because the entire system depends on the extra cooling to keep the temp within reason.

I found that that the electric fan on the front of the condensor was not running....no power to the fan...I ran the pwr wire back to the fire wall and then it goes into a huge wire bundle...the wire is good to that point.
What controls the fan??? I wired the fan so that it runs all the time and the a/c works great....just can't find what pwrs the fan...any ideas??

I have a 350 pre-vortec i don't know if that would make a difference, but my idle temperature is about 45 degrees, and my highway speed is 40-41 degrees. I recently replaced everything in the A/C system minus the pipes, maybe that's why.