![[a/c pressure switch]](images/ac_pump_2.jpg)
Tired of having that silly air conditioning in a topless/doorless Jeep? Or maybe you're just willing to sacrifice a creature comfort in order to gain an awesome on-trail tool. Either way, if your Jeep came from the factory with air conditioning, you have the makings of an excellent on-board air system, with fewer headaches than adapting a compressor from another application.
Some ingredients of an effective on-board air system are common to every installation, while others are 'nice to haves'. The must haves include a pressure switch and a safety valve. One major 'nice to have' is a tank. I'm currently running my system without a tank, which doesn't seem to affect performance much, when filling tires. If I were trying to use air tools, the absence of a tank would be much more noticable.
The first step in doing this project is designing the system. A couple decisions need to be made, for instance where you will put switches and safety valves, or if you will have a tank or not. If you choose to include a tank, where will you put it? I've seen applications with the tank under the hood, above the rear axle, or 'create-your-own' tanks such as roll cages or bumpers. Note that pressurized air can be a dangerous thing. Be very careful how much you use, and what kind of container you use to store it.
There are two huge bonuses to using the factory air conditioner compressor for building your on board air system. The pump/compressor is already installed with the proper brackets and belts for your motor, and the wiring you need is already in place. When you get to stage two of the project, you will be removing certain pieces of the existing air conditioning system, while leaving others in place. I cut both hoses that connect to the a/c pump. One of these goes to the firewall, the other to the system pressure switch. From the pressure switch (which is attached to the passenger side front fender), hose runs to the condensor, in the grill. Coming out of the condensor, a second hose runs to the firewall. Cut both hoses at the firewall. Unplug the pressure switch, and remove it and the condensor. Note that in the picture, I've spliced the pressure switch wires together. I did this for testing purposes, to ensure that the magnetic clutch on the pump worked and that my switch wiring worked. When finishing the system, I wired an air pressure switch here [see below].
![[a/c dash wiring]](images/ac_dash.jpg)
Inside the tub, there are four screws holding the air conditioner to the dash. Behind the controls, there are two sets of wires. Note which wires connect to the on-off swicth. These wires will be used for an in-dash on-off switch. I used a lighted switch from Radio Shack. Remove the air conditioner housing (the piece that holds the switches, fan and vents), pulling the hoses through the hole in the firewall. There is a little piece of metal with a rubber gasket to seal the firewall holse for the hoses. I removed that and cut a little piece of sheet metal and used silicone and a couple screws to cover & seal the hole.
Now that the useless pieces are out of the way, its time to install the pieces that make the compressor a useful Jeeping tool. Initially, I had planned to install a tank to the jack bracket on the passenger fender. The tank I acquired for free didn't fit, so for now I don't have one. When I get a new front bumper, I'll plumb that as a tank.
![[completed system]](images/ac_pump_done.jpg)
Since the jack bracket was now available, I figured I'd just attach my pressure switch & air manifold to that, using hose clamps. I used the wires from the factory pressure switch to connect my switch. The one I bought turns on below 80 psi and off at 120 psi. The output hose from the pump connects to a 'T' fitting, to which are connected the pressure switch and one to three manifold. To the manifold, I connected a pressure gauge and an ouput hose, which I ran through the grill and has a quick-connect fitting on the end. The third opening in the manifold is reserved for a 200psi pop-off safety valve (150psi would be better). To finish the system off, install an air filter on the pump intake line. I used a slick little K&N filter - but cheaper alternatives, like lawnmower air filters, work well too. When on the trail, I usually leave the pressure switch set to 'Auto'. That way, when I need air on the trail, I just hit the dash switch to get the system running - without having to pop the hood. On the road, I keep both switches set to 'off' since its rare that I need to use the air.
![[coil connected to air output]](images/air_hose.jpg)
For filling tires, I have a 25 foot coiled hose with quick-connect fittings on both ends (one male and one female). I connect this to the output hose at the front bumper and use a tire-fill fitting on that. The coiled section stores conveniently, but also reaches all tires, including the spare. I also have a 'blower' fitting to put on there, but haven't needed it too much so far.
To keep your compressor happy, you'll need to lubricate it regularly. In the stock configuration, the refrigerant would properly lube the pump. Since you'll be running fresh air through it, you'll need to supplement its diet with some kind of oil. I've used regular motor oil and Marvel Mystery Oil, both of which have worked for me. The safest bet for longevity would probably be to use air compressor oil, since thats what its designed for. After extensive use, I pull the air filter, dump a little oil down the intake and run the compressor for a little bit to distribute it.
So, how does it work? Exceptionally well, even without the tank. A few days after finishing, I drove to Moab, to test it out. On the trail, I had some tire issues (10 psi seems a bit low for my 32s - I blew a bead or two) and the compressor really saved the day. Its so nice to be self-sufficient for that stuff on the trail. The compressor put out enough oomph to re-seat a bead, though it wasn't off the rim too badly. It also makes airing up at the end of the day a quick job. In terms of performance, it seems roughly equivalent to a York system, and thats compared to one that does have a tank. At 1500 rpms, the gauge reads 80 psi throughout the tire fill. If I just put the air blower on the end and let it free-flow, the gauge shows a constant 40 psi.
This summer (2000), at a club run in Grand Rapids, Minnesota, another club member blew the bead on his 35" tires. My little underhood compressor reseated that thing in no time flat! (hee, hee)
Looking for more info? I've saved a bunch of emails on the subject from different mailing lists. You can see them here. Also check out the following sources, which have great diagrams & text:
Thanks to the following folks for hints, parts and help: