I have replaced all of the hoses, the thermostat, flushed the entire system, and I know the heater core is not plugged. I also put on a new radiator cap. The vehicle isn't overheating, it just won't blow hot air inside the cabin. The lever to change from hot to cold air seems to be working. I can see the lever move, and it sounds like a flap/door moving. I am stuck. Help me please.....
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Re: 1992 Jeep Wrangler with no heat in cabin
It dosen't happen often, but the air intake side of the core can become obstructed with leaves etc. If that is the case, the only way I know of to fix it is to remove the core & clean it. You did check the heater control valve to make sure it is allowing proper coolant flow through the core, right? Did you run it after refilling the system with the cap off and the heater on high to purge any air in there?
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You may want to check the two water houses that feed the heater core. they both have to be hot. (they are usually located next to the thermostat housing.) If they are cold first check the coolant level. Fill up if needed, then you may have to check of there is an obstruction by the housing or the heater core is clogged up. I would first disconnect the hoses and see inside the thermostat housing with a lamp. Also blow some Air inside the heater core to see if flushing is needed. Well if those hoses are both hot then that must be a problem inside the cabin with the vents selection. Either an electric switch or cable. But there are already a few things to check first.
once engine is hot
all cabin setting set to heat
check hoses going into cabin from engine - are they hot if not check - engine thermostat.
flush cabin heater core with water from garden hose - through both core hoses one direction then the other - to clean out core.
check vacuum doors in heater core box in passenger compartment.
Thermostat.? if you haven't? Do it first then try it. While the car is running for a while touch the heater hoses that lead to the firewall. if one is cold and one is hot? You have a blocked Heater core. Follow the hoses back to the engine. Unconnect them both. By using a garden hose flush out the heater core do one side and then reverse by doing the other hose Lots of junk will come out so be care ful. Mistake people make is "Flushing the system" That doesn't mean your flushing the heater core. Seeing that you have done everything else it could be the thermostat which you didn't list or the heater core being clogged. When you finished installing the thermostat and flushing the heater core out. Replenish the coolant system . If you have a bleeder on the thermostat housing? use it . loosen it and top off the fluid until you see fluid comeout of the bleeder. The system being air bound would cause no heat..
If there is a thermostat installed in the engine (195f) and the engine comes up to temp (about 210f) then the problem is likely either an internally blocked core or a bad blend door inside the box. I'd flush the core first by putting flush directly into the core with both hoses disconnected from engine ends.Likely you have a control valve on one of the heater hoses as well they can stick but for most, failure "default" position is to the heat side. Keep the hoses above the core and fill through one end till it comes out the other hose. Wait about a half hour then drain and flush with a garden hose in both directions. If blend door vacuum motor is malfunctioning or door is stuck inside box that is not fun to do. You will need a manual for instructions (haynes or chilton are OK for that) and you need to set aside an entire day for the project.Manual is good for many other projects and so is not a bad thing to have.(about $20) good luck
Run it for a while and check the two heater hoses to the fire wall for the heater core. Turn the heat inside on low and floor. The hoses (when the jeep is hot) should be about the same temp. One will be slightly cooler than the other one. If this is not the case and one is much colder than the other you have a plugged heater core. Mark the cool hose let the jeep completely cool remove the cold hose and the hot hose use a garden hose to flush the core in direction of the cold side to hot side. If this is not it you have a air pocket in the system or your blend doors in the air box under your dash are broke.
The only reason it won't blow hot air is because the water is not getting to the heater core. Check to see if you have a heater control valve in one of the two lines to the heater core. If so check to be sure that is is opening and closing. If it won't open then you get no water flow in to the heater core.
Have the cooling system pressure tested. If it holds pressure, that's a good thing. If it doesn't hold pressure, you may have a leaking head gasket. What may be happening is the crack in the head gasket could be blowing hot air into the cooling system causing it to overheat.