Sunday, 12 April 2015

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?

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 penningthe 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 vacuumto the controls or to the actuator.

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.

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!!!

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.

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.

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