2000 XLT 5.4 Heating troubleshoot

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door54

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Front heater core gave out after 22 years and I got after replacing it once I studied enough UTube videos to find common denominators about the teardown process. It was a bit of a beast to say the least. I was not rushed nor did I try to expeditie the job. Some things just take time if its your first rodeo. After reassembly and only several screws left over the result was mixed. The rear/auxillary heater works well. All dials work as they should. The front however did not blow hot..only cold. The command switch for floor vent/dash or defrost works as it should..just not hot.
Until one day a few days later ..hot air began flowing out of the front. I had left the temp control dial to full warm. and was stoked when it finally kicked in. It stayed good for a few days when I thought it best to dial over to cold air to see how it would respond when turned back to hot. It did not respond back to hot air. Just blows cold now. The rear is still performing as it should...hot or cold on command
Looking for ideas friends...your thought would be appreciated.
Thanks
 

Zharmad

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Based on the intermittent heat, it's likely that you either are low on coolant or still have air in the coolant system that's getting trapped in the front heater core.

Start with checking your coolant level in the front overflow tank and ensure it's topped off. If it looks full, elevate the front end of the vehicle on ramps, start the car and let it run with the heat blasting on in the front and the cap off the overflow tank. If you see the coolant level start to drop then you're replacing air in the system with coolant, just keep it topped off while the engine comes up to operating temp to ensure that the thermostat opens completely (or if you're in a rush, just remove the thermostat and wait longer for the engine to warm up.)

The front heater core sits at a high point in the coolant system and if you can get the overflow cap above it, you can purge the air easier.

Double check you hooked the heater core hoses up correctly, it should still flow though and produce heat either way though.
 
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door54

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Thanks for the solid response. I'll definately get after that soon as I get it back from the driveline shop. When it rains it pours.
 

Vincent Vega

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Also check your vacuum lines. On my 04, and I think your Gen 1, HVAC controls are vacuum powered. You might have accidentally yanked off a vacuum line while replacing the heater core. On my 04, the (black) vacuum supply line goes through the firewall right next to the heater core thrugh the same grommet as the white vac line going to the hot water controller. I had HVAC problems after replacing my timing, figured out I effed up the vacuum supply line while fighting with the RH valve cover. Anyway, check to make sure your HVAC system has vacuum and take it from there as needed. Another possibility: heat distribution blend door actuator (seeYoutube for diagnosing issues with that). You will likely nail this by checking vacuum, cooling system, and blend door. Good luck, let us know what you find out.
 
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door54

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Thanks for the additional response. When my Expy is back in the driveway I'll get after it asap keeping your suggestions in mind.
On the vacuum line connection location...do you know if its accessible without removing the dash again? God I sure hope so... heh
 
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