Question about 1999 Chevrolet Silverado 1500

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1999 chevy silverado heater fan only blows cold air , both coolant lines in are hot

Heater doesnt blow heat, only cold air, the coolant lines by the fire wall are hot and the switch that changes air direction isnt working either ?

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I like that you were knowledgeable to check both coolant lines tells me you are getting hot coolant through the heater core next thing to check will be the blend door on the inside of your vehicle. The blend door is a door that switches from cold air duct to heater duct depending on what you are using at the time. If it is stuck on the cold air duct you will not get any heat sometimes these doors are vacuum actuated and sometimes they are electrically actuated most the time you are able to see the movement of the motor from inside if you don't see any movement but you hear it move chances are it is the door blend I hope this helps.

Posted on Jan 16, 2013

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Take the heater core lines of the water pump and push some water threw the lines or use some air and blow the lines out with low pressure

Posted on Mar 24, 2013

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Posted on Jan 02, 2017

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SOURCE: No Heat and Overheating in 1999 Chevy Silverado

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.

clarkco

Posted on Feb 02, 2009

emissionwiz
  • 76164 Answers

SOURCE: 1999 1500 silverado heater

Sounds like the blend door in the ducting has failed, this door is what controls the temp of the outlet air by blending heat and outside air or AC cooled air.

Posted on Nov 07, 2008

  • 3 Answers

SOURCE: 2004 Chevy Silverado Heater blows cool air

Check blend door actuator for operation

Posted on Feb 15, 2009

  • 3 Answers

SOURCE: NO Heat in 1999 CHevy SIlverado

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

  • 272 Answers

SOURCE: 1999 Chevy Cavalier A/C blows hot air

More likely the recharge blew a o-ring and you have a leak. When your Cavalier was blowing hot air and a recharge fixed it that means it was low on freon which lets o-rings dry out, go back to the shop and have them leak test it. They use a pressurized dye to find the problem. If it's blowing it's not the cooling fan relay, they may have meant compressor relay but I'd have a leak test done first it's not expensive and easier that chasing unknown possibilities.

Posted on Jun 03, 2009

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Sounds like the blend door is not moving. Most blend door actuators are located on the bottom of the heater box near the middle of the car. If the temp control is a round knob, it is an electronic actuator.

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If you know for a fact the compressor is running and one of the lines is cold, I would look for a blend door problem. The blend doors direct air thru the heater and evaporator.

Aug 31, 2012 | 1999 Chevrolet Silverado 1500

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This will help.Thanks.

Mar 27, 2012 | 1994 Volvo 960

1 Answer

My 1999 S-10 does not continually blow hot air when the heater is on. It will often only blow cold air and then the engine temp will rise to an uncomfortable level (almost red line), but then the heat...


Hi, check your coolant level. When the coolant level falls below a certain level the heater core is bypassed. It would also explain your truck overheating if the coolant level was low. If your coolant is that low, check to see where the coolant is going. External leaks are not too bad, but those engines (4.3 and 2.2) were prone to internal gasket leaks also. Check your oil, it shouldn't be milky white.

Jul 23, 2011 | 1999 Chevrolet Silverado 1500

1 Answer

I changed my heater core in my 99 chevy silverado what a job it still doesnt blow hot air what did i do wrong


MAKE SURE ALL BLEND DOORS UNDER DASH WORK PROPERLY. GOOD LUCK MOTOR62500. PS ARE BOTH HEATER HOSES HOT?

Dec 19, 2010 | 1999 Chevrolet Silverado 1500

3 Answers

Would the heater control valve malfunctioning make the engine overheat blowing hot air out the heater one moment,then not blowing the hot air, temp gage spikes 225 plus. The motor takes awhile to heat up...


Heater control valve malfunction will not cause engine to overheat unless coolant is leaking externally...Overheating going down the road can be the result of a few different things...Partly clogged radiator...Insufficient air flow due to possible fan problem...External coolant leak...Make sure fans are operting properly and have cooling system pressure tested for leaks...Gaining and losing heat on the inside of the vehicle usually means system is low on coolant but you must find out where coolant is going

Jan 06, 2010 | 2004 Chevrolet Impala

1 Answer

Heater blows cold air for 20min then blows hot


There are a few things that can cause this problem. Reason #1 a low coolant level can cause the heater core to receive less coolant flow hence causing the heat to come less quickly. reason #2 sticky heater control valve, if this control valve is stuck closed coolant cant enter the heater core hense wont heat up the cabin, reason #3 clogged heater core, over time some heater cores will clog up even sometimes start to leak in cabin. All these are normal circumstances and should be checked. Good luck

Dec 07, 2009 | 1999 Chevrolet Silverado 1500

1 Answer

My heat blows hot for about 5secs then grt cold again whats that


If there is no sign of coolant loss (air pocket in heater core),then check for plugged heater core. Both hoses should be very close to same temp with engine at operating temperature with heater fan on high setting.If the return hose is alot colder, then coolant flow is restricted.

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