Wow! Awesome write up! Good job!
Now sell a bolt on kit like you have made.
Now sell a bolt on kit like you have made.
-
May's Cummins of the Month is now open for VOTING!
Onboard air compressor powered by Cummins
22
When I bought this truck back in November, my girlfriend Lauren asked if I was going to put an engine-driven air compressor on it. Why would someone ask that? Well, I have onboard air on three of my Scouts, and I installed a system on her diesel Scout Terra, too. So she knows that it’s a pretty handy thing to have. But when she asked I laughed and said “No, there’s no way to do it on this truck; just not enough room.” But that got me thinking: Maybe it is possible?
So, after many hours of R & D, I was able to install a Sanden compressor that not only fits, but runs off a single belt. No second belt, no hybrid pulley, and no relocating any of the stock accessories. I can reinstall the stock belt without changing anything. The alternator is in its original stock position.
Three of my previous OBA setups use York compressors, and one uses a Sanden compressor. Traditionally, most OBA setups have used the York compressors, but they are becoming more scarce, and the Sandens are more common (and more compact). The main difference, besides overall size, is that the York compressor is a two piston reciprocating design, and the Sanden has seven pistons connected to a wobble plate. The two types are lubricated differently: the York compressor has an oil sump like an engine, and the Sanden is lubricated by the oil circulating along with the refrigerant in an A/C system. So the Sanden doesn’t hold lubricating oil inside, but blows it out with the compressed air. Oil has to be added to the Sanden to keep it lubricated. Some folks have set up lubricators in the suction side, and others have used grease, but I just check and add oil when needed. There is a special dipstick for Sanden compressors for checking the oil level. I’ve been doing it this way on one of my Scouts for 15 years now, and it works great. The compact size of the Sanden, and the fact that an extra compressor came with the truck, made it an easy choice to go with the Sanden for my Cummins.
Compressor mounting and belt setup:
Removing the engine lifting bracket and upper alternator bracket leaves a nice flat boss with seven tapped holes. There are three 10mm-1.5 and four 8mm-1.25.
I transferred the hole pattern to a piece of 3/8” X 5” flat bar which serves as the compressor mounting bracket. A second piece of 3/8” flat bar is used as a spacer to allow the compressor mounting bracket to clear the water neck.
With the bracket bolted to the engine, I could then line up the compressor and determine the hole locations for the compressor mounting bolts. I drilled and tapped the holes in the bracket to accept 8mm-1.25 bolts. 1 inch long spacers were welded to the bracket. Another bracket was made to replace the upper alternator mount.
Compressor installed. Again, this compressor is identical to the A/C compressor used on the truck.
Idler pulley installed between the fan pulley and the new compressor. This allows the belt to clear the water neck, and also gives the belt more wrap on the fan pulley. The bracket for the idler attaches to two existing 8mm-1.25 tapped holes in the front of the block.
New belt routing.
With the new compressor and idler pulley installed, I used a string to measure for the new belt. I measured a total length of 112.5 inches which is 31.5 inches longer than the stock belt. A Gates K081124 belt is just right.
Electrical:
A toggle switch inside the cab serves as the main ON/OFF switch for the system. The toggle switch gets power from the cigarette lighter circuit which is only hot with the key on. This prevents the compressor clutch from draining the batteries in case the system is left on accidentally. The switch activates a relay which sends power to the pressure switch. The pressure switch is connected to the compressor clutch coil. When power is present at the switch, it will engage the compressor clutch whenever the pressure falls below the cut-in point. When pressure exceeds the cut-out point, the pressure switch opens and the compressor clutch is disengaged. This cycle will continue according to air usage and keep the system between 80-100 PSI as long as the toggle switch is on and the engine is running.
Plumbing:
I found these fittings (this is an assembly of two fittings) which are field repair fittings for the A/C compressors used on the Dodge CTD. They are listed for Freightliner trucks, but it’s the same compressor. These fittings bolt to the compressor head and accept common #8 and #10 A/C beadlock fittings.
The inside of the #8 discharge fitting just happened to be the right size to tap for 1/4” NPT. After tapping the hole, I screwed in a 1/4” NPT to -8 AN adapter.
A small filter is attached with a #10 beadlock fitting to the suction side of the compressor for clean intake air.
I used stainless steel braided PTFE (Teflon) hose with AN fittings for the first part of the system between the compressor and control components. Compressed air can be quite hot, so the hose has to be able to withstand high temperatures. This hose is rated for 400° F. and 2000 PSI. I could have used hydraulic hose, but this stuff looks trick!
For the rest of the system , 1/2” air brake line was used with push-to-connect fittings to plumb the air tank and quick connects.
A coalescing filter is installed between the compressor and the check valve. This filter traps any liquids (oil and water) from the compressed air. The liquids drop into the bowl which has an automatic drain valve. Whenever the pressure drops to zero, the drain valve opens and drains out any trapped liquids. The baby bottle connected to the drain lets me see how much oil has blown out of the compressor.
Edit: After operating the system for the first few cycles, I found that excessive oil was being released along with the air through the unloader valve. For some reason the oil was getting past the coalescing filter, perhaps because the pressure switch is below the filter in this setup. This has never been a problem in the system on my Scout. I had read about blocking a port inside the compressor body to prevent oil from being discharged along with the compressed air, so I decided to try it. Removing the head and valve plate allows access to this port in the compressor body. The port lets oil pass between the lower and upper ends of the cylinders. Blocking the port keeps oil from mixing with the discharge air. After doing this mod, I’m no longer seeing any oil at the unloader valve when it opens.
This is the hole to be blocked. It’s the only passage between the lower and upper ends of the cylinders other than the cylinder bores. The hole is at the 12:00 o’clock position; the compressor is upside down in this pic. I tapped this hole to 1/16”-27 NPT and installed a pipe plug.
Aluminum manifold for the pressure switch and related components, tapped with 1/4” NPT holes.
Manifold with components installed: safety pop-off valve, pressure gauge, 80-100 PSI pressure switch with unloader, and check valve with unloader port.
When the pressure switch opens and cuts current to the compressor clutch, it also opens the unloader valve. This releases all air pressure in the system upstream of the check valve through its unloader port. This lets the automatic drain in the coalescing filter open, and also prevents the compressor from starting up against pressure the next time it engages.
Brackets for air tank. The curved pieces are a mounting kit I bought with the tank, and the flat bars w/studs are homemade.
Brackets bolted up.
Air tank bolted to outside of passenger side frame rail.
Quick connects for air hose at front and rear of truck.
So, after many hours of R & D, I was able to install a Sanden compressor that not only fits, but runs off a single belt. No second belt, no hybrid pulley, and no relocating any of the stock accessories. I can reinstall the stock belt without changing anything. The alternator is in its original stock position.
Three of my previous OBA setups use York compressors, and one uses a Sanden compressor. Traditionally, most OBA setups have used the York compressors, but they are becoming more scarce, and the Sandens are more common (and more compact). The main difference, besides overall size, is that the York compressor is a two piston reciprocating design, and the Sanden has seven pistons connected to a wobble plate. The two types are lubricated differently: the York compressor has an oil sump like an engine, and the Sanden is lubricated by the oil circulating along with the refrigerant in an A/C system. So the Sanden doesn’t hold lubricating oil inside, but blows it out with the compressed air. Oil has to be added to the Sanden to keep it lubricated. Some folks have set up lubricators in the suction side, and others have used grease, but I just check and add oil when needed. There is a special dipstick for Sanden compressors for checking the oil level. I’ve been doing it this way on one of my Scouts for 15 years now, and it works great. The compact size of the Sanden, and the fact that an extra compressor came with the truck, made it an easy choice to go with the Sanden for my Cummins.
Compressor mounting and belt setup:
Removing the engine lifting bracket and upper alternator bracket leaves a nice flat boss with seven tapped holes. There are three 10mm-1.5 and four 8mm-1.25.
I transferred the hole pattern to a piece of 3/8” X 5” flat bar which serves as the compressor mounting bracket. A second piece of 3/8” flat bar is used as a spacer to allow the compressor mounting bracket to clear the water neck.
With the bracket bolted to the engine, I could then line up the compressor and determine the hole locations for the compressor mounting bolts. I drilled and tapped the holes in the bracket to accept 8mm-1.25 bolts. 1 inch long spacers were welded to the bracket. Another bracket was made to replace the upper alternator mount.
Compressor installed. Again, this compressor is identical to the A/C compressor used on the truck.
Idler pulley installed between the fan pulley and the new compressor. This allows the belt to clear the water neck, and also gives the belt more wrap on the fan pulley. The bracket for the idler attaches to two existing 8mm-1.25 tapped holes in the front of the block.
New belt routing.
With the new compressor and idler pulley installed, I used a string to measure for the new belt. I measured a total length of 112.5 inches which is 31.5 inches longer than the stock belt. A Gates K081124 belt is just right.
Electrical:
A toggle switch inside the cab serves as the main ON/OFF switch for the system. The toggle switch gets power from the cigarette lighter circuit which is only hot with the key on. This prevents the compressor clutch from draining the batteries in case the system is left on accidentally. The switch activates a relay which sends power to the pressure switch. The pressure switch is connected to the compressor clutch coil. When power is present at the switch, it will engage the compressor clutch whenever the pressure falls below the cut-in point. When pressure exceeds the cut-out point, the pressure switch opens and the compressor clutch is disengaged. This cycle will continue according to air usage and keep the system between 80-100 PSI as long as the toggle switch is on and the engine is running.
Plumbing:
I found these fittings (this is an assembly of two fittings) which are field repair fittings for the A/C compressors used on the Dodge CTD. They are listed for Freightliner trucks, but it’s the same compressor. These fittings bolt to the compressor head and accept common #8 and #10 A/C beadlock fittings.
The inside of the #8 discharge fitting just happened to be the right size to tap for 1/4” NPT. After tapping the hole, I screwed in a 1/4” NPT to -8 AN adapter.
A small filter is attached with a #10 beadlock fitting to the suction side of the compressor for clean intake air.
I used stainless steel braided PTFE (Teflon) hose with AN fittings for the first part of the system between the compressor and control components. Compressed air can be quite hot, so the hose has to be able to withstand high temperatures. This hose is rated for 400° F. and 2000 PSI. I could have used hydraulic hose, but this stuff looks trick!
For the rest of the system , 1/2” air brake line was used with push-to-connect fittings to plumb the air tank and quick connects.
A coalescing filter is installed between the compressor and the check valve. This filter traps any liquids (oil and water) from the compressed air. The liquids drop into the bowl which has an automatic drain valve. Whenever the pressure drops to zero, the drain valve opens and drains out any trapped liquids. The baby bottle connected to the drain lets me see how much oil has blown out of the compressor.
Edit: After operating the system for the first few cycles, I found that excessive oil was being released along with the air through the unloader valve. For some reason the oil was getting past the coalescing filter, perhaps because the pressure switch is below the filter in this setup. This has never been a problem in the system on my Scout. I had read about blocking a port inside the compressor body to prevent oil from being discharged along with the compressed air, so I decided to try it. Removing the head and valve plate allows access to this port in the compressor body. The port lets oil pass between the lower and upper ends of the cylinders. Blocking the port keeps oil from mixing with the discharge air. After doing this mod, I’m no longer seeing any oil at the unloader valve when it opens.
This is the hole to be blocked. It’s the only passage between the lower and upper ends of the cylinders other than the cylinder bores. The hole is at the 12:00 o’clock position; the compressor is upside down in this pic. I tapped this hole to 1/16”-27 NPT and installed a pipe plug.
Aluminum manifold for the pressure switch and related components, tapped with 1/4” NPT holes.
Manifold with components installed: safety pop-off valve, pressure gauge, 80-100 PSI pressure switch with unloader, and check valve with unloader port.
When the pressure switch opens and cuts current to the compressor clutch, it also opens the unloader valve. This releases all air pressure in the system upstream of the check valve through its unloader port. This lets the automatic drain in the coalescing filter open, and also prevents the compressor from starting up against pressure the next time it engages.
Brackets for air tank. The curved pieces are a mounting kit I bought with the tank, and the flat bars w/studs are homemade.
Brackets bolted up.
Air tank bolted to outside of passenger side frame rail.
Quick connects for air hose at front and rear of truck.
1 - 20 of 92 Posts
1 - 20 of 92 Posts
