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Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1031
Experience:  ASE and Chevy Master , 31yr Dealership exp,
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Chevrolet Silverado 1500 i have a 1994 chevy silverado 4.3liter

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i have a 1994 chevy silverado 4.3liter v6. i do not get heat to the inside. flushed the radiator, disconnected the inlet and outlet hose to the heater core and flushed through it. replaced the thermostat. the blower motor works and blows out cold air to the defroster,thru the vents and on the floor. the hose in and out of the heater core is hot. how do i get heat? is something not opening, if so how do i get to it work.

Hi my name is XXXXX XXXXX Your complete satisfaction is my goal. Please provide as much information about your concern as you can


Is this a manual heat, a/c system or is it an electronic control head?


Sorry , hit wrong button. this is an information request. do not hit accept!! until we diagnose the concern. Thank You. Hal

Edited by Hal on 1/13/2011 at 12:31 AM EST
Customer: replied 5 years ago.
electronic control head i guess. there is no vaccum hoses behinh the glove box.

Ok, if you have the glove box out, look to the left behind dash. there should be the temp actuator. It is most likely stuck in the cold position. Put the temp control in the hot position, with the key on. Take the end of a screw driver and just tap on the actuator.


If it starts to move then replace the temp actuator. It has a sensor in it that can corrode, and not allow it to move. Tapping on it helps it make contact, and will allow it to move.


Try this and let me know your results. You have done everything right so far by what you described. The temp door is just not moving to the heat position.


The temp actuator is #61 in picture.






Customer: replied 5 years ago.
hello, Hal that did not work. The blend/temperature actuator was not the answer. Replaced it with a new one and it did the same. I could here the door open and close and watched the indicator move. It blows air out like it suppose too. Top,bottom and middle. Air still COLD.

If the air door can be heard moving, then the water must not be flowing through all the heater core tubes . ( just going in and out) ( just to make sure I understand you correctly, You can see the temp door motor move from cold to hot, correct??)( look at the shaft to see if it turns)


Can you verify the heater core is getting HOT. It is on the bottom of the case on the rt side.

If you remove the lower cover you can see the heater core. Just put your hand on the lower case on the rt side .

Does it feel hot?? It should If hot water is flowing through the core.


Here is another picture of the case. #25 is the cover I want you to feel for heat. The heater core is directly above this cover.





Don't just go out and buy parts, test it as i'm am instructing you to. I want to help diagnose this with you so your not wasting money,


Let me know what the results are.


Thank You Hal

Customer: replied 5 years ago.
If it's not hot. What to do next?

You have to remove that lower cover and inspect the heater core, and most likely replace the core. Heater cores can just flow enough water to fool you in thinking they have good flow. 3/4 of the core could be totally plugged off and still flow some enough to have hot water on both sides of the heater hoses.


TEST FIRST, verify there is no hot water flowing through the core. You can remove the screws holding the cover up , and just pry it down enough to see and get your hand on the core. you will be able to tell for sure then .


The back screws are difficult to see and to get to. You most likely will not get to the rear left screw. ( that is ok, it will drop down enough to get the core out.) Even if the lower case cracks , it is still ok. just seal the crack up with evaporator tape, available at parts stores.

Customer: replied 5 years ago.
Will try when the weather breaks again

Sounds good, just keep me in the loop , on what your results are.


Keep warm and have a good evening.


Customer: replied 5 years ago.
Hello Hal I am back. Did what you said and it was not warm. Removed it from the truck today. Flush water thru it. Did not see any rust or anything.

I would still replace the core. If you did not get heat at the case, then the core inside may be plugged , but may have one or two cores open that will flow water.

If hot water is getting to the core, and the hose coming out is warm, then the core should be warm to. If it is not getting hot then the core is restricted, and needs to be replaced.


If this core has plastic tanks on it, you can pry back the tabs and remove the tank to see how much of the core is plugged off.



Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1031
Experience: ASE and Chevy Master , 31yr Dealership exp,
Hal and other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
Hello Hal. You said dont waste money. I flushed the core with a very weak caustic solution and flushed it out with a acid base. Cleaned the outside with the same weak caustic solution. Hooked it up to the hoses outsidde of the compartment and ran the engine until it got hot. The core and hoses got hot to the touch.Thanks for your help.

Thats great!! Good Idea, I am glad you have the knowledge to use these chemicals to get the result. Good job!!!!

Have a great weekend.


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