2003 Chevy Tahoe 5.3L.
Dear BL: when i turn on the a/c it makes a clicking noise and it only gets cold if you are driving and rear ac does not get cold at all as long as you are driving it is cold in front but if you stop ata light it does not stay cold and you can still hear the clicking sound thank-you.
Answer: Todays ac systems can be very complicated. Some systems use several controllers,  sensors, switches, relays and modules. Especially automatic, dual zone, and front/rear systems.
To start with the basics, low freon charge is usually the reason for insufficient cooling.  Normally low freon charge will give poor cooling under all driving conditions.
You mentioned a clicking noise. If it is repetitive and coming from the dash area, a  common problem is one of the blend/mode door actuator motors.
Sometimes when they fail, they randomly search for a position.

There are also a few bulletins for ac problems.......
1- The low pressure cycling switch in the receiver/dryer may malfunction. Sometimes a lite tap can help diag.
2- Adding an auxiliary fan in front of condenser
3- May also be a control head reprogram update.
Would recommend having a dealer technician look at it. There may be trouble codes  stored, and a technician will most likely have to look at several different data  parameters to diag. Properly.
1999 Tahoe 4w/d 5.7 Vortec.
Changed gear box, EVO sensor, Front end parts inspected aligned front end rotated tires.Question = Steering very loose at all speeds. Wants to wander.
Answer: This is a complaint heard a lot on these style Tahoe's. If you're absolutely sure that all the front end components are good, and have no excessive play, you should check to see if there is any play in the front hubs. That is all that is really left that may cause a steering issue. If you have the stock size wheels and tires, it may be an issue you just have to deal with. A steering shaft replacement could probably tighten it up a little bit, but may not be enough to be noticeable.
2002 Chevy Tahoe 5.3 liter v8
Question = Where is the low pressure air conditioning valve located  on my 2002 Tahoe. I see two valves on the high pressure side(small diameter line), but none on the low pressure (large diameter line).
Answer: The two fittings that you see on the smaller line are what you're looking for. They are on either side of the orifice tube, so one valve is high pressure and the other is low pressure. You can hook up an A/C machine at that point, or if you're topping off the refrigerant with a can, attach it there as well. You will notice one valve is larger than the other, which is they way to tell high from low pressure. Make sure you check the sticker for the amount of R134A that the system takes.
Chevrolet Tahoe Clicking Boise In Dash, A/C Blows Warm

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