HVAC Control Wiring Question - Coolant Heater/Circulator

RPhil

Adventurer
Hello All,

I have a 2000 Ford Excursion (manual HVAC controls as opposed to the newer digital controls that came in those trucks). It has a front and rear HVAC system. I would like to utilize the heater cores and fans in the vehicle while parked and camping/sleeping.

Would it cause any issues if I were to supply the HVAC fan circuits with an alternative 12 volt source? If I supplied the proper circuits, would I be able to utilize the dials inside the vehicle? I am not sure if there will be any backfeeding issues or any other electrical concerns of which I should be made aware.

My plan is to plumb in a coolant heater (Espar, Webasto, etc.) into the coolant loop of the truck. I would plumb it upstream of the heater cores so that it would circulate the coolant through them. I would like to run the HVAC fans in order to use my heater while the vehicle is off (and I want an alternative source - "house battery" - to perform this task so I do not drain the starter battery). The purpose of this exercise is to be more comfortable while sleeping in the back during camping sessions. I think it would be a much cleaner solution than utilizing a standalone heater. An additional benefit is that I would be able to plumb in a heat exchanger into this circuit to take showers as well.

Kind Regards,
-Russell
 

shade

Well-known member
I'd figure out your power budget first. Running fans like that can burn through a lot of battery power. Knowing how much will allow you to size your house battery appropriately, and you may find that it isn't practical.
 

RPhil

Adventurer
I'd figure out your power budget first. Running fans like that can burn through a lot of battery power. Knowing how much will allow you to size your house battery appropriately, and you may find that it isn't practical.
Good point. It looks like both the front and rear are fused at 40 amps, which is high. That would have to protect against the fans at their highest speeds. I would keep them on the lowest setting. My google-**** is having trouble finding out amp draws- I'll keep researching and potentially test myself if needed.

Does anyone have any insight regarding issues with backfeeding through these circuits? I would need to send power to the blend door potentiometer and the mode selector switch.
 

Attachments

Rando

Explorer
Unless you add some diodes or a relay, you will be backfeeding every 12v circuit in the vehicle. Also, the fan motors in most older vehicles are speed controlled with a series resistor - so running the fan on low doesn't really save any power - it just dissipates power in the resistor as opposed to the fan.

Honestly, this doesn't sound like that practical a solution.
 

dreadlocks

Well-known member
I'm planning something like this for my Diesel Westfallia project.. the advantage I have over you is I'm converting from air cooled to water cooled, so I'll be adding heater core w/blower.. I'll be using a marine one like this, uses less than an Amp of power: https://www.kent-marine.com/en/product/4966/blower-heater-helios-2000-12-v-2000-w.html

I'll also wire blower up to a thermostat so it dont have to run continuously.. you also have to calculate the coolant heater needs power too, the fuel pump and potentially water pump also take power.. all that starts to add up fast if your not careful.. My westy has dual GC2 house batteries and a small deka starter battery so its got a considerable power bank compared to most
 
Last edited:

Rando

Explorer
Thats just protecting the conductors. Hard to say, but fan itself probably draws no more than 10A or so.. but you really need to open up stuff and measure current draw of the appliances you want to use.
It may turn out impractial if the OEM stuff draws more ’aux battery power than you are willing to provide.
Disagree with that, it should only backfeed whatever is on the fan/accessory circuit.
Depending where the ’foreign’ power is introduced, it may be alot of, or just a portion of the ’acc circuits. Much depends on how the ’acc circuit is broken up by relays or other switching.
Probably yes, but you really need to see a schematic of the car or open up and see how its wired.

As far as prevent backfeeding.
One simple solution is use a form ”C” toggle switch.
Throw the switch one way to power from OEM. Throw the opposite way to power from ’aux.

Unless he cuts a bunch of wires or adds diodes/relays, everything will be back fed. The blower motor power comes from 'hot at all times' and the control circuitry comes from 'hot in run', both of these will need to be powered to have the blower work and the control dial work. If you want the controls to work, It is not as simple as just wiring the blower to the aux battery. It can be done but it will take some work to it right, and I am guessing it will use a lot of power. Not completely clear from the diagram, but it looks like the blend doors for the mode selection are vacuum actuated, so those won't work without the motor running.
 

RPhil

Adventurer
Thank you all for the insight. I have some more research to do, I have come up empty in finding a free pdf of the entire wiring on my vehicle, so I will look to buy one on eBay. I don't mind cutting a bunch of wires at all.

You are right on the blend doors, I overlooked the fact that I would need to run power to the vacuum pump- they are vacuum actuated. It is probably a better idea to ensure the blend doors are in their desired position before I turn the vehicle off and resort to auxiliary power.

I would like if this project worked out, it seemed more unique than the cheap diesel-fueled heaters that have become popularized. Based on some of these hurdles, it may be my best bet. But it isn't fun to be like everyone else!

It seems like the easiest solution is to ensure my heat temperature setting and vent setting (both vacuum actuated) are in their desired positions before I turn the vehicle off. Then, I could send power directly to the blower motor(s) (probably only use the rear heater core blower as the power usage seems higher than I anticipated) and place a diode to prevent backfeeding.
 
Last edited:

dreadlocks

Well-known member
Your a gasser? Oh so the thing is Diesel Engines dont produce very much waste heat at all.. so much that w/out emissions gear you can idle a diesel engine all day long and it'll never reach operating temps.. so this is why Diesel powered rigs will go through the trouble of adding a coolant heater, you'll get instant defrost and heat without waiting 20mins of driving and scrubbing your breath off the windshield in the meantime, driving a diesel in the winter can be quite brutal and remote starts wont do anything for em.

Now if you have a diesel + camper, it makes even more sense just re-do your entire HVAC system around a diesel fueled coolant heater, then for your trouble and expense you get instant heat on cold starts, cabin heating when parked, and with another heat exchanger even some hot potable water...

If your on a Gas powered vehicle, your better off getting a Gas powered Air Parking heater that has its own blower and does not require you to completely redesign your vehicles cooling loops.. or even a separate fuel like a LP Propex heater w/a horizontal tank under the truck/van, either option will be cheaper, simpler, and easier.. you have little real need to pre-heat your coolant as your engine will warm it all up in 5mins of driving, or 15mins of idling.
 
Last edited:

rayra

Expedition Leader
already planning to do the same in my suburban. I'm just adding a rear power switch / rheostat to feed power to the squirrel-cage fan on the rear AC setup. Putting a diode on the factory power line connection to the fan to prevent backfeeding any of the factory circuitry. Camp in the back, turn the switch on, air blows / sucks thru the second row ducting. Power drawn from my isolated Aux / house battery.
I've already added / changed some wirign back there to provide two sepate LED strips, switches in the D-column.
I have to open that all up again when I finish my rear bumper winch cabling and replace my backup camera. and route wirign from my rooftop solar / roof rack. Have to take out the rear platform and drawers to do all that, so I'm doing several projects at the same time while I have things all apart.

In the Sub there's a constant-hot PowerPort in the passenger side cargo area trim panel. Lots of room for mods in there. I've got some pics in a topic somewhere when I was sound-insulating the rear cargo floor, sidewalls and wheel tubs, showing the overall rear AC setup. I don't expect other rear-air vehicles to be much different. I'll try to find those pics.

here's a few that don't really answer anything, other than it's easy / possible to mod whatever you want, once you take things apart.


 

Rando

Explorer
Thank you all for the insight. I have some more research to do, I have come up empty in finding a free pdf of the entire wiring on my vehicle, so I will look to buy one on eBay. I don't mind cutting a bunch of wires at all.

You are right on the blend doors, I overlooked the fact that I would need to run power to the vacuum pump- they are vacuum actuated. It is probably a better idea to ensure the blend doors are in their desired position before I turn the vehicle off and resort to auxiliary power.

I would like if this project worked out, it seemed more unique than the cheap diesel-fueled heaters that have become popularized. Based on some of these hurdles, it may be my best bet. But it isn't fun to be like everyone else!

It seems like the easiest solution is to ensure my heat temperature setting and vent setting (both vacuum actuated) are in their desired positions before I turn the vehicle off. Then, I could send power directly to the blower motor(s) (probably only use the rear heater core blower as the power usage seems higher than I anticipated) and place a diode to prevent backfeeding.
Another thought - how are you going to isolate the rear heater core from the rest of the coolant loop?
 

rayra

Expedition Leader
Here's the image I was thinking of.



Any rear air vehicle will be similar. A heater core, an AC coolant exchanger, a plastic duct body, a rear intake vent, and a simple blower motor. Put a diode between the factory power line and the original power connection and add a new power line to the original power connection. With the new power coming from a rheostat switch so you can dial up the fan speed. That power preferable coming from an Aux / House source and not your primary battery.


eta
ah you want heat, not just airflow. Good luck with an electric heater, takes a LOT of juice, especially if your vehicle isn't running and providing either charging or heating coolant.
 

RPhil

Adventurer
Your a gasser? Oh so the thing is Diesel Engines dont produce very much waste heat at all.. so much that w/out emissions gear you can idle a diesel engine all day long and it'll never reach operating temps.. so this is why Diesel powered rigs will go through the trouble of adding a coolant heater, you'll get instant defrost and heat without waiting 20mins of driving and scrubbing your breath off the windshield in the meantime, driving a diesel in the winter can be quite brutal and remote starts wont do anything for em.

Now if you have a diesel + camper, it makes even more sense just re-do your entire HVAC system around a diesel fueled coolant heater, then for your trouble and expense you get instant heat on cold starts, cabin heating when parked, and with another heat exchanger even some hot potable water...

If your on a Gas powered vehicle, your better off getting a Gas powered Air Parking heater that has its own blower and does not require you to completely redesign your vehicles cooling loops.. or even a separate fuel like a LP Propex heater w/a horizontal tank under the truck/van, either option will be cheaper, simpler, and easier.. you have little real need to pre-heat your coolant as your engine will warm it all up in 5mins of driving, or 15mins of idling.
Yep, gasoline, but eventually swapping in a cummins and 6 speed.

It is looking like it may be significantly easier to just get a standalone air heater and then plumb in a basic plate heat exchanger in the engine compartment for hot showers. Like you said, would only need to idle for a relatively short period of time to get that coolant warmed up.

already planning to do the same in my suburban. I'm just adding a rear power switch / rheostat to feed power to the squirrel-cage fan on the rear AC setup. Putting a diode on the factory power line connection to the fan to prevent backfeeding any of the factory circuitry. Camp in the back, turn the switch on, air blows / sucks thru the second row ducting. Power drawn from my isolated Aux / house battery.
I've already added / changed some wirign back there to provide two sepate LED strips, switches in the D-column.
I have to open that all up again when I finish my rear bumper winch cabling and replace my backup camera. and route wirign from my rooftop solar / roof rack. Have to take out the rear platform and drawers to do all that, so I'm doing several projects at the same time while I have things all apart.

In the Sub there's a constant-hot PowerPort in the passenger side cargo area trim panel. Lots of room for mods in there. I've got some pics in a topic somewhere when I was sound-insulating the rear cargo floor, sidewalls and wheel tubs, showing the overall rear AC setup. I don't expect other rear-air vehicles to be much different. I'll try to find those pics.

here's a few that don't really answer anything, other than it's easy / possible to mod whatever you want, once you take things apart.

---
Good information, thanks. Are you just planning on using that fan to circulate the air? Have you found any information on power draw of your fan?

Another thought - how are you going to isolate the rear heater core from the rest of the coolant loop?
From my research, the Espar and other brand coolant heaters produce more output than I will need for just the rear circuit, so I was considering just heating the entire vehicle coolant loop to prevent short cycling. When I was first thinking about this, I didn't really consider that information. Could also loop in a calorifier as well.

But, to answer your question, it is easy enough to add a couple manual ball valves if I wanted to isolate just the rear loop for whatever reason.
 

rayra

Expedition Leader
Good information, thanks. Are you just planning on using that fan to circulate the air? Have you found any information on power draw of your fan?
I'll report on the amp draw of the blower fan at both low and high speed when I get it apart. Easy enough to put a meter on it then. I don't expect it to be more than 5amps, but don't know for sure until it's probed.
If you find a circuit diagram for your vehicle you can trace it back and see what the circuit is fused at and use a majority portion of that number to rough-calc your battery life.
I'll be running wire for mine from my Aux, so not too worried about the load.

I don't have the equations handy right now, but I've never seen an electric heating source really pan out in a regular vehicle install. Resistance heating takes a lot of juice. If you want heat inside a vehicle you're probably better off with a small MrHeater/ Little Buddy propane tent heater, it's CO2 safe and shuts off if knocked over. It would be far easier to rig a bracket to hold such a small gas heater off of a seat headrest post or shoulder belt mounting bolt, inside a vehicle and be as toasty as you care to be for little propane use.
all you'd need is a sort of cupholder bracket sized to fit a 1# propane cannister. and with enough standoff to keep the hot part away from your upholstery / interior plastic.

Too, common propane torch canisters use the exact same attachment / tank valve and the are small enough and tall enough that they'd probably work just fine in a vehicle cupholder withOUT any bracket fabrication. So all you need is a ceramic / catalytic header head, on a torch tank.
Only downside is condensation / moisture, and keeping a window cracked. Or good for a warm-up before bed and after waking up. Not realyl supposed to run tent heaters in a sealed up tent, either.

/other options / ideas


eta

 
Last edited:

RPhil

Adventurer
I'll report on the amp draw of the blower fan at both low and high speed when I get it apart. Easy enough to put a meter on it then. I don't expect it to be more than 5amps, but don't know for sure until it's probed.
If you find a circuit diagram for your vehicle you can trace it back and see what the circuit is fused at and use a majority portion of that number to rough-calc your battery life.
I'll be running wire for mine from my Aux, so not too worried about the load.

I don't have the equations handy right now, but I've never seen an electric heating source really pan out in a regular vehicle install. Resistance heating takes a lot of juice. If you want heat inside a vehicle you're probably better off with a small MrHeater/ Little Buddy propane tent heater, it's CO2 safe and shuts off if knocked over. It would be far easier to rig a bracket to hold such a small gas heater off of a seat headrest post or shoulder belt mounting bolt, inside a vehicle and be as toasty as you care to be for little propane use.
all you'd need is a sort of cupholder bracket sized to fit a 1# propane cannister. and with enough standoff to keep the hot part away from your upholstery / interior plastic.

Too, common propane torch canisters use the exact same attachment / tank valve and the are small enough and tall enough that they'd probably work just fine in a vehicle cupholder withOUT any bracket fabrication. So all you need is a ceramic / catalytic header head, on a torch tank.
Only downside is condensation / moisture, and keeping a window cracked. Or good for a warm-up before bed and after waking up. Not realyl supposed to run tent heaters in a sealed up tent, either.

/other options / ideas


eta

Thanks for the information, looking forward to your measurements.

The Espar isn't really an electric heater, it uses some power of course for operation, but it is a fuel-fired coolant heater/circulator. The startup electrical power will be high, then it tapers down to a lower amp draw for operation.

If only money weren't an object and the Espar and a large capacity house battery were cheap... I can dream.
 

rayra

Expedition Leader
Thanks for the information, looking forward to your measurements.

The Espar isn't really an electric heater, it uses some power of course for operation, but it is a fuel-fired coolant heater/circulator. The startup electrical power will be high, then it tapers down to a lower amp draw for operation.

If only money weren't an object and the Espar and a large capacity house battery were cheap... I can dream.
I intend to tear into the back end of the Suburban starting on the 9th, I'll report back on the amp draw then.
 

Forum statistics

Threads
180,065
Messages
2,806,496
Members
215,271
Latest member
WanderingVWBus
Top