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Bob
Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience:  Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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Started blowing..blowing cold air..a heater core stop..2000Silverado

Customer Question

My truck also just started blowing cold air even with the heat setting all the way over to full hot. How could a heater core stop up when it was working great a couple of weeks ago.
It's a 2000 Silverado with 115K. Help !
Submitted: 7 years ago via CarComplaints.com.
Category: Chevy
Expert:  Bob replied 7 years ago.

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.

Customer: replied 7 years ago.
Reply to Bob's Post: The engine gets up to normal temperature and stays there. I already checked the hoses going into the firewall and yes, they are both equally hot/warm. When turning the temperature control know back and forth there is no sound at all of a door opening/closing. No sound at all. You mention a cable being broken but do not tell me where it is or how to fix it.
I'd be very happy with this service if I was given a way to fix it. It does not seem to me that the heater core could be plugged up if both lines get hot. The only other thing I noticed was that the button that switches back and forth for recirculating inside cabin air flashed and would not change for a couple of days too, but that started working.
Expert:  Bob replied 7 years ago.
HiCustomer Sounds like you are correct. If both hoses are hot, that would eliminate the heater core. I believe that the heat mode door on your truck is controlled by an electric stepper motor and not a cable. I'm sorry part of the previous post was pretty generic. Let me take a look at the GM web site and see what they say about diagnosing the mode door and I will post it here as soon as possible. Thanks.
Customer: replied 7 years ago.
Reply to Bob's Post: Ok. Let me know. If you can figure out something I can do I will not only accept and pay but I have another question to ask that I would pay for too ( separately so you get paid twice ) if I could request you get the question.
Expert:  Bob replied 7 years ago.

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.

 

Document ID# XXXXX

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

 



Condition

Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent.

Cause

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.

Correction

  1. Remove the Air Bag fuse.
  2. Disconnect the steering wheel and instrument panel (IP) air bag connectors. Refer to the SIR subsection of the Restraints section of the Service Manual for connector locations.
  3. Remove the IP upper trim pad.
  4. Locate connector C206 (6 cavities) or C296 (8 cavities). The connector is attached to a metal brace on the far right side of the IP carrier above the IP air distributor duct.
  5. Inspect the routing of the wiring harness to the connector. The proper routing of the wiring harness is above the air distributor duct with no tension on the terminals in the connector. The routing is improper if the wiring harness is below the air distributor duct with excessive tension on the terminals in the connector. The excessive tension may cause poor terminal contact, resulting in open circuits, in the connector. The wires may also pull the terminals out of the connector or pull out of the terminal itself.
  6. If the harness is routed properly, contact Technical Assistance for further information.
  7. If the harness is misrouted, remove the connector from the brace.
  8. Disconnect the connector.
  9. Perform a pin drag test on the female terminals.
  10. Inspect the male terminals for straightness.
  11. Inspect the wire to terminal connection to insure that no wires have pulled out of the terminals.
  12. Reroute the wiring harness above the air distributor duct.
  13. Firmly reconnect and reseat the connector.
  14. Reattach the connector to the metal brace.
  15. Reinstall the IP upper trim pad.
  16. Turn Off the ignition and reconnect the steering wheel and IP air bags.
  17. Reinstall the Air Bag fuse.
  18. Turn ON the ignition and verify that the air bag light flashes seven times and goes out.
  19. Clear any diagnostic trouble codes that may have been set.
  20. Verify proper operation of the HVAC system mode and temperature controls.

Warranty Information

For vehicles repaired under warranty, use:

Expert:  Bob replied 7 years ago.

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.

Document ID#(NNN) NNN-NNNN
2000 Chevrolet Chevy K Silverado - 4WD

 

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)

 

 


Condition

Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent.

Cause

An HVAC control module logic lock-up may be the cause of these conditions.

Correction

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.

Part Information

Part Number

Description

15126606

Cadillac, Celsius Temperature Display (RPO U34)

HVAC Control Assembly (Module)

15126605

Cadillac, Minus (-) Celsius Temperature Display (RPO U34)

HVAC Control Assembly (Module)

15126604

Chevrolet/GMC, Celsius Temperature Display (RPO U34)

HVAC Control Assembly (Module)

15126603

Chevrolet/GMC, Minus (-) Celsius Temperature Display (RPO U34)

HVAC Control Assembly (Module)

Parts are currently available from GMSPO.

Expert:  Bob replied 7 years ago.

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.

Customer: replied 7 years ago.
I have no idea what you are talking about with class 2 scanners or stuff like that. However, I will go ahead and accept your reply so you can get paid. Just send me back one more mail saying ok or something and I'll accept. You sure deserve that problem solved or not. One other quick question though. When I started the same truck this afternoon I noticed that there was quite a lot of liquid coming out of the tailpipe to the point of running down the driveway like a leaking water hose. I do have the Orange Dextron antifreeze but this stuff had absolutely no smell or color at all. Some small whiffs of white smoke ( like a blown head gasket ) but only when I revved the motor up pretty good. Anyway write back and say something so I can accept your answer next time.
Expert:  Bob replied 7 years ago.

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.

Temperature Control Cable Replacement

Removal Procedure

  1. Remove the radio.
  2. Remove the heater control assembly.
    Object Number: 363029  Size: SH

  3. Disconnect the temperature control cable from the heater/ventilation module.
  4. Remove the temperature control cable from the IP carrier.

Installation Procedure

  1. Install the temperature control cable to the IP carrier.
    Object Number: 363029  Size: SH

  2. Connect the temperature control cable to the heater/ventilation module.
  3. Install the heater control assembly.
  4. Install the radio.

Document ID# XXXXX
2000 Chevrolet Chevy K Silverado - 4WD

Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience: Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
Bob and 3 other Chevy Specialists are ready to help you
Expert:  Bob replied 7 years ago.
As to the leak, first thing to do is verify that you are not loosing coolant. If you are not, then chances are good it was just condensation collected in the catalytic converter. But if you have lost any coolant, that could also account for the heater problem if it is circulating air in the system. If you have lost coolant, you will need to do a pressure test on the system. Best if you could do it with the plugs removed and look for coolant in any of the cylinders or on the plugs. I would also inspect it for coolant in the oil, just to be safe. A leaking intake gasket could also cause this kind of a problem, so it pretty much hinges on if you have lost any coolant or not. But even if you have not, I would keep an eye on it for a while. Even condensation in the cat converter could blow out white smoke because of the heat developed. Let me know, I will still be here if you have another question or need more help.
Customer: replied 7 years ago.
Reply to Bob's Post: I paid the initial $9 and put in a $10 bonus for you. I hope that is acceptable. Thanks for your time !
Expert:  Bob replied 7 years ago.
Very, very much appreciated. You were most generous. If I can be of further help, just post here and the system will notify me. Thanks

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