All I get is cold air. My system is the mechanical one on the 1996 Grand Cherokee Laredo 4.0L 6 Cylinder. When the Jeep is running and warm the temp gauge is working, the blower switch is working, the selector switch for floor, defrost, etc. works in all positions. But no warm air, only cold is blowing. Have checked the little 10amp fuse but it is ok. I got a Hanes Jeep book from the library, but it only told me how to disassemble everything to get at the heater core. Any easy way to tell if this is the problem? My Jeep doesn't leak coolant and has new radiator hoses on top and below. That heater core is in a horrible place. Any way to know what is at the cause. Thanks, JIm
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Re: heating system blows only cold air
It maybe a blend door problem. if both hoses at the firewall for the heater are close in temperature its not likely a heater core. the actuator for the blend door is located on the bottom of the heater/ac box towards the middle of the bottom. it will be a tight fit but you can remove it without removing any part of the dash. take it off and disconnect the power. start the vehicle and manually move the door and see if the temp changes
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If you put the thermostat in correctly (spring towards the engine) that should be OK. Likely if the water pump wasn't leaking or had a bad bearing, you wasted your $ on that. If you re-filled it and did not have the heater on high heat, you may have some trapped air in there. But, still overheating says another thing. If you have a blown head gasket, it can pump compression into the cooling system and drive the coolant from the core. It will also overheat. You can have that tested at most any decent shop that will do a hydrocarbon test to find that.I think someone makes a chemical test kit for that but not sure if it's very expensive or not. White smoke from tailpipe will also be an indicator as will be any coolant in the engine oil or coolant on one or more spark plugs. If it turns out that it has a head gasket problem don't stop looking for problems as often a faulty fan or obstructed radiator can cause the initial overheat that caused the gasket to fail.
Generally this condition is the result of coolant loss, or failed thermostat. If coolant goes below cylinder head level, or thermostat remains closed,heat will stop working. Do not drive with this condition as excessive heat buildup in cylinder head can and will do serious damage to heads and or head gasket. Find out where leak is and correct it. Change thermostat as it may also be damaged. Check for excessive steam from tailpipe or miss in engine, as these symptoms indicate a cylinder head problem.