A/C Cold While Slow: Warmer at Speed

[Stratosurfer]

All,
the '97 Tahoe's A/C throws out ice cubes at slow speed and idle (below 50F air), but at freeway speed apparently the compressor is cycling off more than necessary to keep those ice cubes coming. My Mr. Goodwrench said there is an adjustment on a switch or a different switch somewhere to keep the compressor running longer at freeway speed, but he quit the business before handling the problem last summer.
Anyone know what adjustment on which switch or switch change out is required to keep the coldest air coming at freeway speed if the stat is cranked all the way down?
Thanks

[More Power]

The refrigerant charge is probably not right, or there might be moisture in the system that blocks the orifice under certain conditions.

Jim

[Stratosurfer]

The refrigerant charge is probably not right, or there might be moisture in the system that blocks the orifice under certain conditions.

Jim
I checked the charge, it's spot on. Is there any adjustment (pot?) to keep the compressor on longer or did I get bad data. If it' really cold at idle the numbers should be close on charge/moisture/oil in the system ect: correct? Former mech said that as the speed is so much higher at freeway rpms and speed that some switch will cycle off the compressor just based on revs and speed to compensate for the higher rate of spin and cooling on the condensor coil, not necessarily the T-Stat readings. I normally run the T-Stat max cold and fan wide open on recirc.
Anyone???...

[More Power]

You can buy an A/C test kit at Wal-Mart. This'll allow you to evaluate the system cycle pressures. The kits include instructions that'll help you decide if the compressor is cycling correctly. You may have a low-side switch that cycles either too high or too low. The test kit will tell you that. :)

Jim