Introduction: Aftermarket Car A/c Wiring

I have a 20-year-old Ford van with 175k miles. I've owned it for 10 years and intend to keep it as long as it runs.

But last year the a/c went out [big hole leaking freon somewhere] and I refused to fix it because of the cost and the age of the vehicle.

This year I didn't want to sweat it out like last year, but the cost and age still make it a big risk and I don't have the money to gamble. Plus, any repair expense would be lost when the vehicle is sold or scrapped. All I get out of fixing the a/c is cool air for a while.

I have seen conversion vans with window a/c's that had a genset on the van to power them. It would be cheaper to fix the a/c than to go that way. I have 2 sine wave inverters that see occasional use and had already wired one to the van for light duty tool use. That 600 watt inverter was not even close to being able to power a 5k BTU 120v window a/c. The other inverter, a 1k watt ProSine inverter from Home Depot was theoretically large enough, so I went ahead and went back to Home Depot and bought the smallest/cheapest window a/c they sold, an LG LW5015E.

The inverter is connected to the battery with a set of jumper cables I cut the clamps off. The small white box in line with the red wire is a 175 amp fusible link as a fail-safe in case something shorts. The disconnect switch is one I salvaged off a broken portable car jump starter. If I need to disconnect the inverter I don't have to undo battery terminals that way.

The LG window a/c wouldn't budge when I tried to run it. The compressor just hummed and the inverter overloaded multiple ways, so I asked some people at an off-grid forum I am a member of for advice.

Step 1: The Fix

I got 2 suggestions. The inverter was not mounted next to the battery to keep it away from the heat and vibration under the hood. Mounting next to the battery keeps the low voltage dc feed short, but would eventually ruin the expensive inverter.

So, the first fix was to buy a 12v super capacitor assembly from eBay and mount it next to the inverter [which rests on the front passenger seat most of the time]. The super cap assembly I chose can actually start the vehicle. There is a youtube video of someone starting a V8 Dodge Charger with that assembly. It has 6 370F D-cell caps and overvoltage/charge balancing circuits. The supercap assembly is housed in a plastic project box from Radio Shack because there are exposed connection on the bottom of the circuit board. Shorting out a 6-pack of 370F caps would make quite a bang.

After connecting the supercap array to the inverter, the inverter would still not start the window a/c, but the only fault it gave was that it took too long. The inverter is supposed to be able to push 2k watts for about 1 second before going into overload. I had to find a way to either get the start current down or shorten the compressor run up.

The other suggestion I got was to buy a start-boost cap with a PTC and relay. A PTC is a positive temperature coefficient relay It disconnects itself from the circuit after a second or so because the current inrush at startup heats up the internal thermistor. If the start-boost cap stayed in the circuit it would eventually fry either the start or run windings of the compressor. Brand new from eBay the correct start-boost cap relay was only $10 shipped. It has piggyback disconnects so no cutting or splicing of wires has to be done. The instructions say to connect it in parallel with the existing run capacitor on the a/c. The window a/c has a wiring diagram under the cover and it was a simple fix. The start-boost cap was mounted on the outside of the a/c because of it's size.

After doing both fixes, the window a/c will start and run with no trouble [except if I idle for a long time at night with the lights on]. My van's alternator won't put out that much power at low speed, so at night I have to rest my foot gently on the accelerator to get the idle up a bit to keep it all running. If I don't the inverter simply quits as the van voltage sags.

The next part of this project will be to build a box so the a/c hot side will vent out the sliding window behind the driver. I don't want to mount the a/c through the side of the van as that exposes the coils to vandalism.

Step 2: Venting the Hot Air

For now I have positioned the a/c in a box and cut out the box to make a cardboard plenum to connect the a/c to one of the 2 sliding windows the van has. This places the a/c directly behind the driver's seat. I can still see out the back and sides to view traffic, but cannot access the controls on the a/c. The a/c has no remote control, so the fan is set to low and the dial thermostat is set about middle. When I power on the inverter it starts and runs the a/c. The initial wattage is about 460, but rises to over 600 as the a/c heats up. 600 watts is the edge of what the van's alternator can deliver and requires putting the transmission in neutral and gently resting my foot on the accelerator when I stop for a light or in stop and go traffic. At 35 mph and above it just works.

The little blue and white 12v fan redirects the cold air. The a/c vents were not made to send the air sideways like that.

I am considering putting the a/c behind the gap between the front 2 seats and making a curtain out of a sheet of plastic or clear shower curtain. That would blow cold air in the correct direction and eliminate the need for a cardboard duct and 12v fan.

EDIT: I've added a roof vent, shown in another instructable for venting. I just added a 120 watt solar panel and charge controller to boost my van's electrical output when the sun shines. It's hard to keep the a/c running on alternator power at idle waiting for lights. See the next step for pictures of the final install.

Step 3: Adding the Solar Panel and Charge Controller

I found 120 watt lightly used Kyocera panels for $1 a watt (shipped) on eBay.

A cheap charge controller on eBay

The charge controller is needed to avoid overcharging the van battery. I used to have a 5 watt panel that I would plug in while parked at work and set on the roof and even that small panel would overcharge the vehicle battery on sunny days. The charge controller is connected to a 12v 17ah sla like this one

The controller has to be ballasted with a battery whenever there is a panel connected otherwise the panel voltage would damage the controller. The van has dual a/c, radio and cigarette lighter behind the driver's seat for the second row of passengers. I backfeed the van's main battery through the cigarette lighter from the controller, but the smaller battery stays hardwired at all times to protect the controller.

The back of the panel is riveted to a L shaped aluminum rail cut and drilled to replace one of the van's roof rack rails. The front of the panel is wedged under one of the other original roof rack rails and the remaining rack rails have been removed. There is a small amount of shadowing across the panel from the front rail, but it's effect is minor. There are some strips of peel and stick foam under the panel in places to protect the van roof and keep the assembly tight.

When it sunny out the panel provides a boost for the van's electrical output and takes some load off the alternator.