Just changed the water pump and the thermostat. Did step by step in accordance with a Chiltons back yard mechanic book. Got all put back together (with no spare parts) was connecting the negative battery cable back up and there was much clicking coming from the passenger side firewall area. Started the vehicle, let it warm up, put the air on max hot and fan speed hi, checked for leaks (none noted) and took it for a test drive. Air exiting the ventilation got extremely hot. Turned the climate control down to 66 (external ambient air temp was 53) and there was no change in ventilation air. Cycled the air positions (floor/dash vents, floor/defrost, floor, dash vents etc.) and cycled the fan speed. No change in temperature. Returned to house, left engine running, checked for leaks (none noted) and turned off the engine. Left it off for 5 minutes, started it back up, turned on ventilation and extremely hot air again, then it went to a cooler temp and right back to desert hot again. There is a clicking or popping type noise behind the dash somewhere. Any suggestions to what the problem may be? Is this a dealer service only fix? In advance thanks for any posts. 4.3 liter 4WD 121000 Miles, 24000 miles with brand new GM motor.