This morning I headed over to the hardware store to see if they had any 3/8″ fuel line to help adapt the 5/8″ heater hose to the 3/8″ barb. The fuel line was difficult to push onto the barb even with lubrication. In fact I had to use the coolant bottle from my spares that had the barb cut off. This allows the fuel line to barely fit over the barbless inlet. At least it worked. Then with some lube the 5/8″ heater hose fit snugly over the fuel line. A hose clamp made the whole thing water tight. This is what prevented the truck from being finished last night.

The heater element pulls about 8.5 amps at 321vdc. That’s over 2700 watts! The air sure gets warm quickly. On the drive to work I watched the thermometer that I stuck into the vent. It peaked at 130F or so, and then the over temp sensor would shut off the heating element. The temp at the vent would drop to about 105F, then the element would come back on. It was so nice to have a real heater for a change!!!! The bad news is that the heater uses 2.7kwh. So it’s a bit of a load for my small pack.

The original heater hoses were fairly brittle. When I clamped them with long nose vice grips they cracked and leaked. So the heater got all new hoses. I’m a little concerned about using 100% coolant and no water. I may siphon some coolant out and add water. Ethylene Glycol is not as efficient at 100% concentration. I used silica free coolant. A large syringe really helped when I had to prime the pump or remove coolant without any spilling. I used a Dremel tool and fiberglass cutoff wheel to shorten the inboard mounting tab on the Hotstart heater housing. It was a lot faster than using the mill because I didn’t have to figure out a jig. Cut off enough of the tab to just remove the 2 inboard mounting holes and no more. Otherwise there won’t be enough material to keep the seal in compression.

BTW, the heater core tubes coming through the firewall were aluminum. Be careful when adding or removing hoses!

This heater upgrade could really be polished off with a variable temperature control. I thought about it today. The control circuit could be placed with the heater relay in the battery box, or if it fit, into the heater box. The heater box is a bit cramped. I suspect the circuit will need a source of metal around to thermally sink the fets to. The heater box might be too warm, but it would be the most convenient. Maybe the engine compartment is a decent mounting place for at least initial testing. This circuit would also lighten the load on the battery pack by allowing the heater to run at settings less than full current.

The temperature control knob would mount next to the heater button the dash. I think it will fit onto that small cover. An LED would be good to indicate if temperature control is on or not, and at what rate it’s pulsing. Maybe zero to 100hz would do it. The schematic is in pieces but has enough info that I could start on circuit testing in the future.

A lesson learned from an ACP failure that I witnessed, will give the circuit an indicator signal that is actually enabled when there is high voltage present at the output of the fets. This makes sure that if there is a fet failure, that there will be an indicator to tell me that.

I used a Dremel tool and fiberglass cutoff wheel to shorten the inboard mounting tab of the Kim Hotstart heater housing. It was much faster than using the mill because I didn’t have to jig up the heater to machine it.

Don’t forget to prime the pump!! It’s a pain in the butt!! You will smoke your heater if you don’t!!! You can shine a flashlight behind the coolant bottle to make the coolant glow. When you look inside the bottle or through the wall of the inlet, you can see both huge bubbles or microscopic bubbles. Both of them should be moving to show that the coolant is flowing. I used my aux battery to spin the pump without running the heater. A 50/50 mix of coolant and water will help with the priming as coolant is way too thick.