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No Heat!

CBK Lucifer

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Hey guys, this is my second winter with my 77’ 620 Longbed and I think it’s time I spend some time trying to figure out why I don’t have any heat lol. All hoses are connected, I’ve taken the heater face plate off and cleaned out the few leaves that were in there. The air lever slides and opens the control valve (minor antifreeze leak from the control valve, not really sure why, debating on replacing) and I can’t come to a conclusion on why I don’t receive heat. The fan kicks on when I pull the lever outwards but I don’t get heat or any air for the defrost. Should I try to find a new core?


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I’m assuming so? The lower hose exploded into the cab one time going the road so I think so? Lol how would I check if it’s flowing through? Also! I forgot to mention that my engine heats up more than usual when I try to kick the fan on. Maybe it’s backed up somewhere not allowing fluid to travel freely?

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I had a similar problem with a heater on my beater. I reversed the flow to the  heater by disconnecting the heater hoses from the engine and used a garden hose to check flow through the heater valve and core.  If you have a garden hose nozzle that fits the heater hose it makes less of a mess.   If no flow, bypass the valve and try again.  It will be either or both but you will be able determine if it's one or both using this method of elimination. 

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Drain and save the anti-freeze. Set the heater control to HOT so water will flow through it. Take the two hoses off the engine side and use a garden hose to blow water through the core in both directions to clean any sediment out of it. You may have to do it several times but when the water is clean in both directions you're good. Hook up the hoses and refill the engine.


Get or borrow an IR (infra red) gun and 'shoot' the thermostat housing when the engine has been warmed up. It should be around 180F. If 120F the thermostat has failed and stuck open and needs replacing. If the engine isn't warming up, you can't expect the heater to work.

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I had a similar problem after I got my truck. PO said the temp gauge never worked either. Turns out there was no thermostat in the housing. Put a new one in and the heater and gauge started working perfectly! So yeah, make sure your thermostat is working correctly... or exists in general. 

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