The a/c is operating on my 98 tahoe 5.7 4x4,but when I push the recirculation button to get optimum cooling ,the light works but there is no change in temp or blower speed. What should I be looking for or testing? thanks for the help.

You should be able to look under the dash on the passenger side and see the recirc door open and shut. There is a servo motor that operates the door. It may have failed or the door itself is stuck or jammed. Hope this helps!

If your temp setting is at full cold- then you are already in recirc- and hitting the light won't change it--put the temp setting in about halfway mode-- then hit the button- see if you hear it change...

thanks for the replys.I will try that tomorrow.

Also, going into the "recirc" mode will not change the blower setting. If the recirc system is working properly you will hear a difference in air movement.