I have a 2005 Silverado fully loaded with duel control a/c. Sometimes randomly with the temperature set below 70 degrees and inside temperature much higher the Driver side will suddenly start blowing hot air while the passenger side will continue blowing cold air.

Is this a simple inexpensive repair or a costly one left to the experts?

Answer: The most common cause for this problem on your Silverado is that the drivers side temperature door actuator motor is bad. This will cause the temperature on that side to go full hot or full cold. This can happen on the drivers side or passenger side. There is a temperature door motor for each side.

You would need to test for proper voltage into the temp door actuator motor to confirm it is not a problem with the control head giving the wrong signals, but most common is the actuator.

Chevy Silverado Engine Tap Noise 

Question: i have a 1998 Chevrolet z71 with 5.7 liter when i crank it after it sits for a couple of hours it taps like no oil in the heads is my oil pump bad i also have a whine that is consistent with engine speed is that a sign that points to the oil pump?

Answer: No, neither of these problem on your Chevy Truck point to a bad oil pump.

You could have contaminated oil. That would make it thin. That will cause a top end tap. Check for leaking intake manifold gaskets. This would allow coolant to get into the oil.

You could have low oil pressure caused by worn out bearings.

You could have bad lifters that bleed down after sitting and take a while to pump back up.

A whine noise would need to be diagnosed with a stethoscope to determine what is making the noise. It may just be a bad belt, idler pulley or one of the accessory pulleys.