Fixing The Harrison Deluxe Fresh Air Heater.
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The heater fan was intermittent which turned out to be bad contacts inside the fan speed switch. It's a three position switch with wirewound resistors between contacts. It was mounted in the dash hole for the cigarette lighter but I moved the new replacement switch to the bottom of the dash because of reinstalling the lighter socket. The new switch came with a mounting bracket for this purpose.
After hooking up the new switch and testing it, I now know why the original switch was toast. It appears the fan motor is an original 6-volt unit, which explains why the wirewound resistor on the back of the new 12-volt switch was glowing like a toaster element.
The best way to fix this would be to leave the 12-volt switch installed and replace the 6-volt motor with a 12-volt one. If I kept the 6-volt motor and changed the switch to 6 volts, I'd still have to add a whopping big power resistor in series to drop the voltage down. It would better to just install the correct motor, but turns out it's a major job to just get the heater out of the truck.
After hooking up the new switch and testing it, I now know why the original switch was toast. It appears the fan motor is an original 6-volt unit, which explains why the wirewound resistor on the back of the new 12-volt switch was glowing like a toaster element.
The best way to fix this would be to leave the 12-volt switch installed and replace the 6-volt motor with a 12-volt one. If I kept the 6-volt motor and changed the switch to 6 volts, I'd still have to add a whopping big power resistor in series to drop the voltage down. It would better to just install the correct motor, but turns out it's a major job to just get the heater out of the truck.
Once the heater is out, changing the motor is fairly simple, but actually getting it out is neither easy nor simple because of the aluminum plate on the firewall. There's just no easy way to get that plate off now. From pictures I've seen of a disassembled Harrison heater the firewall mounting bracket is spot welded to the heater case and there is a stud on each side of this bracket that goes through the firewall. So the nuts on the studs are under the aluminum plate where I can't get at them. I may have to cut the heater bracket to get it out. Nothing can ever just be easy.
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Even if I don't get the heater out I will still install a heat control valve in the heater hose line so I can adjust the temperature and be able to shut off the heat in the summer when using the fan just for fresh air.
more to come when I can get time to pull the heater out. |
Page created 4/29/2024
Last edited 5/1/2024
Last edited 5/1/2024
