'00 temp gauge + air conditioning

My 00 Monte's temperature gauge goes all the way to the left (somemetimes with an associated check engine light) but only after driving at 60 MPH+ for over 15 minutes or so. When the gauge drops the air conditioner compressor also will not come on. I've changed the temp sending unit in the block with no help. Right now it's 98 in San Antonio and I'm dyin!! Any help?!!

thermostat problem is what it sounds like, replace it and see what heppens, sound sliek its stuck open and cooling down too far

Isn't there a temp sensor in one of the heads too? I may be mistaken.....

I haven't seen a sensor in a head, but I haven't looked either! I'll check it out. Thanks

I know from past experience that on some vehicles, there are 2 sensors, one for the temp gauge, and one for the PCM.

i'm thinking you have a t-stat issue, or a PCM issue. the CEL 'trouble code' would better point you in a direction. i've run into many S-10's with t-stat issues that throw a code for 'unable to regulate engine temp' or something similar. if the PCM see's a drastic change in engine temp, it will disable the a/c compressor, as the a/c system generates a lot of heat thru the condenser. i want to say it only has one temp sensor, as if it had a seperate one for the gauge alone, it shouldn't affect the a/c, just the dash gauge. hope this helps some.