Question about 1999 Chevrolet Silverado 1500

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NO Heat in 1999 CHevy SIlverado

I have no heat in my truck. Blows plenty of air but no hot air. I have changed the thermostat but this did not help. I cannot locate any valve on the heater lines going into the cab. Any ideas?

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  • JOEMYERS56 Jan 18, 2009

    I HAVE CHECKED BOTH LINES ON MY TRUCK AFTER CHANGING T STAT. LINE GOING TO CORE IS HOT AND ONE LEAVING COOL..I PULLED LINE OFF COOLER SIDE AND WAS NOT GETTING A STRONG FLOW FROM THAT SIDE. RIGHT AFTER i DID THAT WE WERE GETTING HEAT. AIR BOUND OR PLUGGED OR CLOGGED CORE......IT'S DRIVING ME CRAZY.

  • furches3458 Feb 07, 2009

    Same problem, no heat. Open thermostat would eventually heat some. Can,t find a valve outside. Is it under the dash?

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Flush the heater out with a hose.   the fastest and cheapest.   if that dosen't work then replace the Air blend actuator motor.  $59.99 at Auto Zone  part    # 604-101

Posted on Feb 27, 2009

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There should be a vacuum controled water valve on this truck it may be laying on the intake up by the front on the passenger side of the engine.(but GM did do away with this on some vehicles and just use the air blend door to keep the heat out of the cab). The first thing I would do is, touch each hose to see if they are both hot after warms up engine. The one come from the engine should be hot if the valve is open. If one is hot and the other is a little cooler or cold you may have a cloged heater core. If both are hot and you have no heat, then the air blend door may not be opening on the inside the heater box. This could be cause by many things. The actuator may be bad that pulls it open, something may have gotten inside the box and penning the door and it will not let it move, to let the heat in to the cab. The heater control itself may be bad. You could also have a broke vacuum line out under the hood or under the dash some where, causing it loose vacuum to the controls or to the actuator.

Posted on Oct 30, 2008

  • Mike Stager
    Mike Stager Sep 26, 2010

    Have had this problem with my mother in laws truck. There appears to be a problem with the heater control switch for the blend door. When set to maximum cool, it overruns the limit switch on the blend door actuator, causing it to bind the gears in the motor. If you pull the motor off ( located under the dash, passenger side middle...3 small screws and an electrical connection ) and disassemble it, you can see what has gone wrong. It's a matter of resetting the gears. You can keep the halves of the motor disconnected, reconnect the electrical and operate the heat control and see what happens. I'm not sure what exactly the problem is, but you can avoid future problems by not turning the heat control to "full cool or full heat" by marking the point to where it won't over run the actuator motor. Otherwise you are going to have to replace the switch control assembly @ $100 . I replaced both the motor and the control with used units and have the same problem a year later.

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After reading on this same sight, I took both hoses off the heater core and flushed both ways with a garden hose particles flushed out when I put the hose on the outlet side. I reconnected the heater hoses and now I have great heat again. Thanks!!!

Posted on Jan 23, 2009

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Providing that you don't have trapped air in the coolant system, it appears to me that you have a "blend door" issue. The air is probably not passing across the heater core because the electric motor that moves the door from the "cold" to "hot" function is bad. I have had to replace these in the past due to this condition. The motor itself is located on the "heater box" beneath the dash. Hope this helps.

Posted on Oct 30, 2008

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My truck has an extremely small leak in the coolant system (just confirmed this past month). If this happens again, you need to only remove the top heater core hose, place garden hose nozzle into the hole of hose you removed and let the flow of water force the air out of the heater core; this is commonly referred to as "burping" the system. It worked perfectly a few years ago, then this month when the temp dropped, I went to use the heater and.. nothing but heat for 5-7 seconds.
Also, if you do not think your heater is working as well as it should.. there could be 'some' air trapped; just enough to interfere with the proper operation. When I 'burped' it the first time, I was really amazed how much warmer the heater was compared to a month earlier.
If you have a dual climate control (as in same model but Surburban) this might not work.

Posted on Oct 21, 2014

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Replace heater core and it will work

Posted on Sep 28, 2014

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In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car. Always have this problem confirmed by a dealer or qualified repair shop as it is a very expensive repair.

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After replacing the thermostat, you must bleed the air from the cooling system.

To bleed air from the 2.2L and 2.5L engines, remove the plug or sensor on the top of the thermostat housing. Fill the radiator with coolant until the coolant comes out the hole. Since the plug is made out of steel and the thermostat housing is aluminum, it is a good idea to apply an anti-seizing compound or Teflon® tape on the plug threads prior to installation. Install the plug and continue to fill the radiator. This will vent all trapped air from the engine.

Any trapped air in the heating system will have to be displaced by coolant. Once the cooling system is filled, with the radiator cap off, turn of the heater at it's highest setting. Start the engine and allow it to reach operating temp. You should see a drop in the coolant level as the air in the heating system is displaced by coolant. Add coolant to the proper level and replace the radiator cap.

Keep a close eye on the coolant level for at least the next couple of weeks. The cooling system is a "closed" system. Any significant decrease in coolant level indicates a problem.

If you have any questions, let me know.

Please take the time to rate this solution.

Drive safe and be warm.

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