So now the Hotstart heater is mounted in the heater box and the whole
assembly is back in the truck. Nice and clean.

As for operation, the ground fault issue appears to be gone. But I did
find what might be a factory defect. When the selector knob is set to
Heat, then by taking the temperature knob and rotating it clockwise
for warmer air, at about 2:30 o’clock the heater element comes on,
then at 5 o’clock the pump comes on. Say what?? The heater element
comes on without the pump coming on. This could be the very reason
that the heater never worked for the first owner. Someone toasted it!
It would overheat itself since there was no water flow. I have a
diagram that shows some changes to that very circuitry. I’ll look into

The Hotstart heater draws 8 amps at 321 vdc compared to 5.7 amps with
the stock heater. It rose the defrost vent temperature from 75F to
135F in just a couple of minutes. Then the built in temp sensor on the
Hotstart tripped and shut off the heater element, but the pump keeps
running. After the defrost air went down to about 94F, the heater
element kicked back in. We’ll see on a cold night if this repeats
itself. 75F ambient is a very hot place to start a heater test. The
great news is I have an original heater in one truck and an improved
heater in another, so performance can be compared.

Again priming the pump was a pain!! The fastest way was to pull a
vacuum on the output hose that comes off of the firewall until I got a
mouthful of coolant. Then it was primed. Yuk. I could see this heater
smoking instantly without the system primed. It might almost be worth
using clear tubing just to see if there is flow.

The bed hinge hardware arrived today. Too bad I’m so tired. I’d love
to get that done so I can get at those batteries. I suspect they are
dried out as the pack voltage is fine, just hardly any amp hours. If I
could get 5 miles out of this pack it would help testing and even
allow a trip to the car wash.

So I get about 2 hours sleep last night. I get back up and start on
the heater. There was some coolant inside the cap that covers the
bottom of the Rusco heater. But it was enough work that I didn’t want
to put the heater box and all of those hose and electrical connections
back yet again to see if a little coolant caused the ground fault.

So I machined shorter the mounting lugs on the one end of the Hotstart so it
would fit in the heater box. The Hotstart required that the water pump
be moved down a couple of inches and angled slightly to line it up
with the opening. That also required the Hotstart to angled as well. A
90 degree bracket had to be fabbed to mount the Hotstart. All of this
required a few holes to be drilled. I finally got very tired at 6am
after working 4 hours, and had to stop. The only thing left is to
crimp the power leads and temp sensor leads to their respective
crimps. It all looks like it will fit nicely. Hopefully this cures the
ground fault issue. I usually hate to guess, but this was pretty
clear, not absolutely certain, that it was a ground fault.

I’m also putting a pair of connectors in line with the high voltage
leads and another one for the temperature sensor. It would even be
useful to put a connector in for the pump since it would make adding
power to the pump during the rather long priming operation, much
easier. It would make it nicer to diagnose an open heater element if
all I had to pull apart a connector and buzz it out. The military
style connectors are a pain to remove to check these very items. So
the connectors make it much easier in the future.

I found out from the original owner that the truck’s AC and heater
have never worked. The AC will be an interesting debug for sure if
this fixes the heater.

Heater Specs: 240vac, 1500w, Brand: Kim Hotstart, Spokane WA, P/N: TPS152GT12-000, On 120F(49C), Off 140F(60C).

The used Rusco heater that I installed worked for a while. The Emeter
shows the current draw to be about 5-6 amps from the pack. But when I
turn the temperature knob down so it electrically shuts off the
heater, the truck faults. According to Dolcom it’s an isolation fault.
An ohm meter from each heater element lead to ground showed about 3-5
meg ohms. It showed infinite resistance when it not installed in the

After rechecking everything, like maybe wet heater element wires, I
turned the key on one more time. It booted. I turned the selector knob
to heat, and rotated the temperature knob to about the 1 o’clock
position and the pump and heater element came on. Rotating the
temperature knob counter clockwise to turn off the heater, faulted the
truck again.

This truck does not have the orange button to push to turn the heater
on. The heater enable is tied into the truck’s factory heater controls.

The most important part of tonight’s exercise was to make sure the
pump was primed so the heater didn’t smoke. It took way longer, and
was far more difficult than I thought, to get the pump primed. Make
sure you can see the fluid running back into the reservoir before
turning on the heater element. The way I fired up the pump separately
from the element was to remove the green relay inside the small gray
plastic box bolted to the side of the heater box. The highest pin in
the relay socket was the normally open connection that went straight
to the pump. Ground was just the heater box surface. A separate 12v
battery came in very handy.

In case this used Rusco heater is really kaput, I grabbed the 1500W
Kim Hotstart heater like George installed last year, and it looks like
an easy fit behind the Dolphin but outside of the heater box. I could
leave the old Rusco heater installed, but move the wires over to the
Hotstart. That way plumbing to the Hotstart would be very easy and
quick. It would just need to mounted to the Dolphin frame or something.

However, if the pump gets moved down about 3/4″ inside of the box and
one mounting ear of the Hotstart heater is cut off, the Hotstart will
fit inside the factory heater box with just a mounting bracket
required. This is food for thought. It would make for a clean install,
but more work. I’d rather spend my time getting the tilt bed hardware
installed if it arrives tomorrow. I’ll see how I feel tomorrow.

The Rusco is rated at 1000w per the label. The Hotstart is 1500w. Both
of those ratings are at 240vac. With 325vdc running through them, the
Hotstart heater would be about 1800 watts. This could be a nice
improvement over the weak factory heater. And as George pointed out,
with a plastic bodied heater, no more ground faults.

The heater element has open circuited on the #2 truck. I took out the
Rusco tank and cannot see how to get the heater element out. A guess
would be that the top or bottom of the tank that unscrews? Or is it a
throw away unit?

I read through a lot of posts about replacing the Rusco water heater.
But I don’t find where anyone actually replaced the element inside the
Rusco heater tank.

I’ll take an input on this one. I want to get it done tonight. I have
a spare Rusco tank, but I’d rather go with new parts.

The Emeter dc-dc had a couple of opens and an intermittent short on
the power leads. Sloppy workmanship. But at least the dc-dc and the
Emeter, actually a Link10, are both working now. Learned how to get
the dash bezel out without removing the shifter housing or the lower
valence. Nice bonus. Of course there are dash lights burned out, like
charge complete and fault. Time to figure out which led’s I used in
the nicad truck and duplicate it.

The heater pump runs but no heater element current draw, usually 6-7
amps from the pack. This truck does not have that orange button
towards the top of the dash to turn on the heater. This truck turns on
the heater when the temperature know is over half way and the selector
is set to heat.

The air conditioning fans on the air conditioning inverter are
running, but no cold air, I think. The air routing into the cabin is
not controlled. I cannot switch from defrost to vents to floor. The AC
is not drawing any significant power.

That Vicor power module under the hood, is a 300v to 12v dc-dc. No
clue what it’s hooked up to. It’s tough to see where it all goes, but
I will find out.

Only 25 batteries in this beast. I need to turn the charger down.

Time to get a Bridgeboard into this thing.

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