Hate to say it, but they can. But first you need to be sure it is full of coolant and not sucking air. Then you need to be sure the motor is getting up to normal operating temp. If those things are right then you need to see if the temperature mode door is opening to let the heat in.
If the motor is getting up to normal operating temperature check both heater hoses when the car is hot. They should both be hot to the touch where they go through the firewall If the are not both hot and equal, the heater core is restricted or plugged. Sometimes they can be flushed out with a garden hose or compressed air, if they are too bad they need to be replaced. The only other thing would be if it has a plastic hot water control valve in the heater hose and it is shutting off the water supply to the core, but I can't remember that model using one. Also if the core is okay, the heater mode doors could be not opening to let the heat into the car. You can check this by setting in the passenger seat and running the temp control lever back and forth from hot to cold and listen under the glove box to see if you hear the door open and close. If not you could have an unhooked or broken control cable, a problem with the control panel or in the mode door itself.
Hi again, I have found a couple of technical bulletins from GM that may help. I will send them to you in separate posts. Read them over and see what you think. I would think if you pull the lower close out cover off the bottom right side of the dash you may be able to see the HVAC case and look to see if the mode doors are all working when you change the controls. Read through these next couple of items and see if the help and please let me know. GM wants you to use a class 2 scanner to test most of the system, a regular code reader won't work because it needs to be able to do function tests. I hope it doesn't come to that, I hope we can find something that you can do yourself. I do not like sending people to the dealer, but sometimes it is the only way.
Subject:Loss of HVAC System Mode and/or Temperature Control (Reroute Wiring Harness) #01-01-39-007 - (12/20/2001)
Models:1999-2002 Chevrolet and GMC C/K Pickup Models (Silverado and Sierra)1999-2002 Chevrolet and GMC C/K Utility Models (Avalanche, Surburban, Tahoe, Yukon, Yukon XL, Denali)2001 GMC Sierra C32002 GMC Sierra Denali2002 Cadillac Escalade, Escalade EXT
Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent.
There may be poor terminal contact and/or bent terminals in connectors C206 (RPO C68 automatic HVAC controls) or C296 (RPO C60 manual HVAC controls). Excessive tension on the wires due to the wiring harness being misrouted in the instrument panel carrier may cause these conditions.
For vehicles repaired under warranty, use:
Before you try this one I need you to look at the RPO code sticker in the glove box. It is a small white plastic card with a bunch of number and letter combinations on it that is a coded list of all the equipment that your truck was build with. If yours has the following code listed, then this bulletin may apply. U34 let me know.
Subject:Loss of HVAC System Mode and/or Temperature Control (Replace HVAC Control Module) #04-01-39-007 - (06/17/2004)
Models:2002 Cadillac Escalade, Escalade EXT1999-2002 Chevrolet Silverado, Suburban, Tahoe2002 Chevrolet Avalanche1999-2002 GMC Denali, Sierra, Yukon, Yukon XL2001 GMC Sierra C32002 GMC Sierra Denaliwith Automatic HVAC System (RPO C68)
An HVAC control module logic lock-up may be the cause of these conditions.
Important: Prior to replacing the HVAC control head, review Corporate Bulletin Number 01-01-39-007 (SI Document ID #845221).
Replace the HVAC control module. Refer to the HVAC Control Module Replacement procedure in the HVAC System -- Automatic sub-section of the Service Manual.
Cadillac, Celsius Temperature Display (RPO U34)
HVAC Control Assembly (Module)
Cadillac, Minus (-) Celsius Temperature Display (RPO U34)
Chevrolet/GMC, Celsius Temperature Display (RPO U34)
Chevrolet/GMC, Minus (-) Celsius Temperature Display (RPO U34)
Parts are currently available from GMSPO.
This is a brief outline of the temperature control. Will see if I can find something related to it that may help.
The Temperature Valve and The Heater Core
The temperature of the air coming from the heater duct and the defroster nozzle is regulated by controlling the relative amounts of warm and cool air coming from the heater module. The temperature valve determines the amount of the total airflow that passes through the heater core.
When the temperature knob in the control assembly is at the extreme left side of travel, the full BLUE, or cold position, the temperature valve stops all the airflow through the heater core. The heater duct and the defroster nozzle receive only unheated air.
When the temperature knob moves away from the full BLUE, or cold position, the temperature valve opens to allow an increasing amount of air to pass through the heater core. At the same time, the temperature valve reduces the amount of unheated air that enters into the mixture. The result is a very responsive control of the temperature of the air discharged through the heater ducts and the defroster nozzle.
When the temperature knob reaches the full RED, or hot position, to the extreme right end of travel, the temperature valve diverts all the airflow through the heater core for maximum heating.
Hot coolant from the engine moves through the heater core and returns to the cooling system when the engine is running.
Also need you to look and see if you can tell if this cable is connected and working, you may be able to see it from under the dash behind the glove box. It goes from the control panel to the heater door control valve. Don't pull the radio is you can see it from underneath.
Document ID# XXXXX 2000 Chevrolet Chevy K Silverado - 4WD