I know the A/C compressor always engages when the heat or defroster is on. I would guess it helps control the humidity. Would there be any problem if I rewire it so the compressor is only used with A/C ?

 

I added a switch on the dash on my '88 for just that purpose. For defroster use, the A/C helps with removing humidity, otherwise it is a waste of fuel to run.
jim

 

That was a common mods i saw on forums when I had my Ram 3500.
It was a weak link for them.
I was thinking about doing it with the van, but hadn't researched yet.

 

You'd lose your ability to control the humidity in defrost mode---IMHO that's slightly "dangerous" as a foggy windshield could be the result. Even if ambient air is relatively dry human respiration can create that same fog which is just one more reason to keep the system as is for now.

The blend door arrangement of the E-Series beginning in '92 really works well to greatly dehumidify incoming air that hits the windshield. Those of us from the 60's recall how tough it was controlling the cold wet air as it hit and condensed on the W/S----not a fun thing to deal with--then or now.

FWIW and mostly relating to gasoline engines the A/C compressor's don't really impact MPG's as much as they once did. When running mine for comfort cooling and at highway speeds (cruise control on) there's almost zero effect on gas mileage. Since I get about 15 MPG's without the A/C on I'm maybe lowered to 14 with it----not a bad minor reduction.

Your own set up with that snake cage might be different but I'll bet not as much as feared. Do you have the stock A/C system and an auxilary rear unit too, both working off the engine-driven compressor?

By contrast Jim's '88 A/C compressor pulled a lot of HP so his modification no doubt works well.

 

That's one of the advantages to living in Texas, JW, we get DRY heat in the summer and even drier cold in the winter (except for those folks in Houston!).

My 88 had the same blend door operation as the later years. The auto makers decided to run the pumps full-time in all modes besides vent or floor settings. One reason was to keep the pump seals lubed with refrigerant oil to prevent early warranty servicing.

Almost all the foreign made cars have A/C switches to increase MPG, those folks pay lots more for gas so for them 1 MPG is a big deal.

Another advantage to switching off the pump is the wear on the clutch. With the clutch cycling constantly while driving while A/C isn't needed is unnecessary wear. jim

 

I've heard Galveston gets humid too, kinda like New Orleans and that general region? Ya'll from The Lone Star state might laugh at Ohio's "heat" but when it hits 90 and/or humidity approaches 65% and above I'm in the A/C, damn the cost of replacement parts.

Then again I've been known to replace the A/C compressors when they've hit about 200K miles. I'm fortunate in knowing how to find good parts cheap and also knowing more than a few very talented mechanics with a ton of equipment that work on the side for not a lot of cash. Recent compressor swap plus evacuation and recharge set me back a whopping $60.

 

True that!

I spent some "formative" years in the Mo. Ozarks hauling to mom and pop stores on the back roads. Drive, unload potato sacks, etc, drive, for 12 hours/day. The summers were brutal, NO A/C in the cab. At least here, when the temps are in the 100's for weeks, the low humidity saves us.

I don't know any mechanics besides my sons. My dad always fixed his stuff and I guess I just never knew there were folks who would fix stuff. Now that dad is gone, I have his tools as well as my own. He always said if he was going to pay someone to buy more tools, he would buy the tools and do it himself. My grandson is already wrenching with his dad so I suspect he will be a "gearhead" as well!

 

I look at it as saving wear and tear on the compressor as thats what went south on the Dodge....I could bypass it on the 5.9CRD...not sure I could on the van.

 

You don't have to bypass it, wiskey. Just put a switch in the wire going to the clutch connector. I wired mine behind the dash panel but I already had it out for other problems. The hardest part is remembering to flip the switch when the thing blows hot on the first summer day and you are wondering why. jim

 

The reason I asked is my bus uses the stock dash evaporator and an overhead rear evaporator system but only has the large side skirt mounted condensing unit so when the compressor is on with the defroster, the 3 condenser fans are not running. With little airflow across the condenser, is that a problem?

 

Ahh, now I understand your setup. If the cooling fans on the condenser are not running then the high side pressure could get excessive. That would lead to compressor failure. I would certainly turn off the compressor running anytime the cooling fans are not on.

The ideal solution would be to put a relay in the compressor circuit that was powered by the cooling fan power. That would automatically solve the issue. jim





Relay cutout for A/C clutch.