When i start my truck i have heat, but as i drive down the road itturns into just warm air. The passenger side of the truck will blowcold air out on the floor when the drivers side just blows out warmair! I have thought it could be the thermostat but if that was the casewouldnt it blow cold air with no warm air?
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pretty vague question...do you have heat? meaning if you switch to defrost does it blow normal heat? If you have no heat anywhere could be as simple as adding antifreeze..if antifreeze level is correct run engine with heater on, locate two hoses that go from front passenger side of engine to firewall(they connect to your heater core). After engine has been warmed up feel the two heater core hoses if one is very warm and the other is not you may have a plugged heater core or an air bound heater core. If heater core is plugged disconnet hoses at engine and send compressed air through the cooler of the two lines to free up any blockage(I adjusted my air output on my compressor to 45psi). After i cleared blockage i sent CLR through it and rinsed it out both ways with a garden hose(i didnt want the clr going through the engine block). I then filled the heater core & lines with antifreeze premix, reinstalled the lines and topped off the resovoir and I had heat...If you do not have a blockage but are air bound I would buy a compression gas tester from your local napa or autzone and test your antifreeze to see if there is compression gas getting into your cooling system. This could be caused by a crack in a cylinder wall or a weak gasket common on the 5.3's and even more common on the 4.8's
does this truck have dual climate or electric thermometer in the heat/ac control panel. if so the elec. therm. may be stuck and not allowing the temp to drop but so low in the truck therefore you get cold air but no heat because the therm. says it is already hot in the truck. hope this helps.
Had the same thing happen to my truck, the blen door actuator is under the console on passenger side, but the heater core is going to be clogged if you dont have any heat coming through, but a/c works..
have you chg. any thing lately like thermostate? added any coolent to system? if not, thermostate could be stuck in the open position. if stuck open, setting still, it will throw heat, but moving coolent flows to fast and does not get a chance to get hot. if you did chg. thermostate it could have a air pocket in the system. and also adding coolent can create an air pockets too. you will know this when your traveling down the road and temp guage fluctuates up and down. witch means air in system.