Heater only blows cold air.....totally stumped

[vashthestampede]

Hello everyone, this is my 1st post through automotiveforums.com. However I am a frequent user on the miata.net community for my project Miata car.

Anyways, I am hoping someone can help me with this ongoing issue. The Envoy is a 99' and has 116k on it. It runs decent for the mileage, and does what I need it to....seeing its my work vehicle.

The heater doesn’t work 99% of the time, and when it tries to blow hot air....its not even close to what it should be. And now with the winter months here...I need to figure this out.

Recently I replaced the intake manifold gasket (what a job ) And I have double and triple checked everything while I was doing the job. The heaters been out for close to a year now....so the gasket job didn’t do it. I took apart the dash, as well as the climate control box and all looked well. IE: no knobs we sticking, no loose or bare wires, etc

The heater hose from the waterpump gets hot, but the other only gets warm. I was going to try blowing air though the inlet on the firewall to the heater core...and see what I get out the outlet. I wonder if it’s just that it is clogged or needs replaced.

Any help, suggestions, or info on this is greatly appreciated!

Vash-

[vashthestampede]

Funny....I got the answer same day from the fellow Miata members. Didn’t even get a bite from the supposed largest online community. As I was snooping around on here it did seem like not to much knowledge was floating around...

To anyone else that would like a response to the common problem...

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1999 GMC Truck Envoy 4WD V6-4.3L VIN W
Vehicle Level Heating and Air Conditioning Technical Service Bulletins All Technical Service Bulletins A/C - Cooling System Overheating/Heater Blows Cold


A/C - Cooling System Overheating/Heater Blows Cold
Notes

File In Section: 06 - Engine/Propulsion System

Bulletin No.: 99-06-02-012D

Date: April, 2002

TECHNICAL

Subject:
Rust in Cooling System, Heater Inoperative, Blows Cold Air, Engine Overheats (Flush Cooling System)

Models:
1996-2000 Chevrolet and GMC S/T Models (Blazer, Jimmy, Sonoma, S10 Pickup)
1998-2000 GMC Envoy
1996-2000 Oldsmobile Bravada
with 4.3L V6 Engine (VINs W, X - RPOs L35, LF6)

This bulletin is being revised to include additional model years. Please discard Corporate Bulletin Number 99-06-02-012C (Section 06 - Engine/Propulsion System).

Condition

Some customers may comment that the heater is inoperative, blows cold air, engine may exhibit an overheat condition or the coolant reservoir has rust in it.

Cause

Vehicles equipped with DEX-COOL(R) coolant, which may have been operated for extended periods of time with a low coolant level, usually in excess of 32,000 km (20,000 mi), may be susceptible to the formation of a rust-like material in the cooling system.

Correction

Flush the cooling system using the repair procedures that follow.

Parts and equipment required/suggested for this correction are listed below.

^ 1 each *Prestone(R) Flush and Fill kit # AF-KITP U.S. (# 00050 in Canada). This kit can be obtained from your local parts supplier and can be used on all vehicles repaired under this procedure. Save it after performing the repair, as it is reusable.

^ 1 each *Prestone(R) Heavy Duty Cooling System Cleaner, GM P/N 12346500 - 1 per vehicle. This cleaner is in powder form and contains a neutralizer. Do not substitute other cleaners. The diluted cleaners that are available in liquid form are not recommended for this repair.

^ 5.7 L (6 qt) of 100% (non-diluted) DEX-COOL(R) coolant (GM Spec 6277M).

^ 1 each new thermostat, GM P/N 12563335.

^ 2 each new radiator cap, GM P/N 15075565. 1 each *Prestone(R) yellow funnel. This funnel can also be obtained from your local parts supplier. It fits snugly into the radiator opening for an easy fill and is reusable.


* We believe this source and their products to be reliable. There may be additional manufacturers of such products. General Motors does not endorse, indicate any preference for or assume any responsibility for the products from this firm or for any such items which may be available from other sources.

Important: Verify the fuel level in the fuel tank. The fuel level should be above 1/4 tank before this procedure is started.

As a precaution, verify the oil level in the crankcase. Add the amount required to bring the oil level into the normal range.

It is recommended the vehicle be placed in a position so that the following are available:

^ A sanitary sewer - not a storm drain, etc.

^ A monoxivent system (if the outside temperature is less than 10°C (50°F)).

^ Hot running water

Notice: Due to the complexity of these procedures, the following repair steps must be strictly adhered to in order to achieve the intended results. Any deviation or substitution may result in sub-standard cleaning/flushing results or system damage.

Diagnostic Procedure

1. Install the Scan Tool. This will allow monitoring of the coolant temperature throughout the procedure.

Caution: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator without causing the solution to boil. Removal of the radiator cap while the engine is hot and pressure is high will cause the solution to boil instantaneously - possibly with explosive force - spewing the solution over the engine, fenders and the person removing the cap. Under some conditions, the engine coolant is combustible.

Important: ^ The installation of a NEW radiator cap at the beginning of this procedure and the second new cap at the end of the repair procedure is necessary in order for the correct pressure to be achieved and for the repair to be completed successfully.

^ The radiator cap is NOT a good indicator of the general condition of the cooling system. Typically the underside of the radiator cap will exhibit a greater amount of contamination than the rest of the system. It is important to evaluate the condition of the cooling system by checking the following before beginning the repair procedure:

2. Remove the radiator cap. Install a new radiator cap, GM P/N 15075565. A properly operating radiator cap is essential for this procedure to work properly. Be sure to wipe off all radiator cap sealing surfaces prior to installation.

3. Start the engine.

4. Using a flashlight or lead light, look into the radiator. From the right side of the vehicle, peer into the radiator toward the left side of the vehicle. Observe the top three rows (or tubes) of the radiator. (It may be necessary to drain off some of the coolant to see the top three rows of the radiator).

If it appears the coolant is able to flow through the third row down from the top, the vehicle should be repaired using Procedure A. If it appears the coolant is NOT able to flow through the third row down from the top, then the vehicle should be repaired using Procedure B.

5. Stop the engine.

Vash-

[maxwedge]

This forum applies to the GMC Envoy 2002 and newer version with the inline 4.2, maybe that was why no replies!!!

[vashthestampede]

Originally Posted by maxwedge

This forum applies to the GMC Envoy 2002 and newer version with the inline 4.2, maybe that was why no replies!!!

I see GMC ---> Then ENVOY. There are no specifics!! There are questions already referring to 99's up to 05's. Don’t blab at me the reason why no one posted like I messed up. This is by far the WORST online community I have ever had the chance to experience. I will go back to my knowledgeable forums now.....

By the way....lol....isn’t it great that when a real solid question is asked...nobody knows shit right. But when I state the fact that nobody knows shit....someone’s a smartass....lol

Vash-

[maxwedge]

Smart ass, your ass, if I had seen this post initially I would have helped. I only interjected that comment as an explanation as to why you may not have gotten a response. The forum moderator should have stepped in here to let you know the focus of this forum was the later Envoy's, for that there is no excuse. Good by then.

[JimmyGold]

Dude, I have a 2000 GMC Jimmy - the same vehicle as your 99 Envoy. Check your coolant, if it's low then top it off. If this helps you might want to go ahead and get a flush, this should work fine.

[vashthestampede]

Flushed the heater core with air then water. Works perfect now. Once again.....this place holds no knowledge....

I did this weeks ago, just wanted to see if in 2-3 weeks anyone has had a clue....but I guess I was right. Thank god I don’t rely on this place for help, you guys are fun to pick at though...lol

Vash-

[blazee]

I'm glad that we could help you.

If there's ever something else that you can't handle, just let us know.

[FormulaLT1]

Originally Posted by vashthestampede

Flushed the heater core with air then water. Works perfect now. Once again.....this place holds no knowledge....

I did this weeks ago, just wanted to see if in 2-3 weeks anyone has had a clue....but I guess I was right. Thank god I don’t rely on this place for help, you guys are fun to pick at though...lol

Vash-

I'm really going to miss you , don't let the e-door hit you in the a$$.

John