RPM's with a/c

[TheApocalyptican]

Going to be buying my tuning stuff soon,and wanted to start learning and looking over stuff now. I was looking over the $42 bin file from this site for a 1227747, and saw both: RPM added to desired idle w/AC on, & RPM added for A/C On. The first has a value of 0, and the second has a value of 25. Why are there two different settings? Do they both need adjusted in some way, or is just the second necessary?
I want to raise the rpms with the a/c on because it makes the a/c work better, and during the summer here in Vegas, the colder the a/c the better.

[PJG1173]

one of the things you have to keep in mind is the descriptions were made by the user community so sometimes there is some ambiguity in some of the xdf's. I have a different PCM and I have idle rpm A/C on P/N and idle rpm A/C on in gear. some times you just have to experiment with the settings and see what they do. I suspect it may be one for ingear and one for out of gear. is the bin for a manual trans?

[EagleMark]

There's actually 6 different scalers for A/C. The 2 you are talking about are for idle and desired idle, Idle would be neutral or open loop. Desired idle would be for Closed Loop idle in gear.

They all work well as is to keep a good steady idle while the A/C compressor kicks on and off. If you have a manual trans raising the RPM is fine. But please take a warning of raising the idle in an Automatic trans! If you raise the idle with A/C on, and are sitting at a traffic light stopped with foot on brake and A/C kicks on and idle increases to much you start to roll into the car in front of you if you do not apply more brake pressure.

These settings are not to make idle rise, but to keep idle steady while A/C compressor kicks on and off. They are useful for off roaders who have on-board air and want idle higher when air compressor is running. But that is always in park or neutral.

[TheApocalyptican]

I figured there had to be a difference between the two. I appreciate the warning, but during the middle of summer here, the a/c almost never kicks off, so it switching back on isn't much of an issue. I did this same thing last summer with the idle screw, and it made the a/c work so much better. I learned however, that with the base idle changed, it messes with the computer, and can make the computer actually pull timing. While I'm not sure if it will actually pull the timing, what I was reading about the computer wanting a specific rpm made sense, so now, I'd like to do it the right way and bump the rpm up some AND let the computer know that is the way I want it.

[EagleMark]

Sounds like a good plan.

I'll tell you I have a 1990 Suburban with four core radiator and shroud with clutch fan. It will idle in parking lot with A/C on at near 100 degree days and keep car cool and not overheat, leaving grandma and dog in truck while we shop. Having good fan and shroud to suck air over A/C condenser is imperative to good cooling at low speeds.

I've also seen guys on net use water injection sprayer nozzles to spray a lite mist of water in front on condenser at idle to further cool when at stop? Like an evaporative cooler (swamp cooler) patio misters and such sold in AZ and areas like you are in. It evaporates before ever coming into engine compartment.

[TheApocalyptican]

I've too got a 1990 Sub with a 4 core and shroud with clutch fan. Also has pushers on the evap in the front. No overheating problems at all this way! I am however running r134a, and I have found that just adding a little rpm...to say like 700, makes the a/c ice cold at idle. The biggest problem here in the summer is that we've got that 100°+ heat, and then all the concrete and blacktop, and I'm sure the asphalt is probably 130°+! Best solution would be to move somewhere cooler, lol.

Thanks for the help on this. Probably will be back with a question or two once I actually start tuning.

[Xenon]

Not to hijack this thread, but are those factory 4 tube radiators you guys are running or did you put them in... Mine has one but I got it out of a '76 and had to fab mounts for it... If they are factory what do the mounts look like?

[TheApocalyptican]

Mine Sub is a 1500 with a 350. The rad in it is for a 2500 with 454. The only mounts I changed were on top of the rad. It went from a one bracket on each side style, to a single one that covers the whole top of the rad and still bolts in where the two singles did. Ordered a brand new one from LMC Truck.
Pic:
http://i231.photobucket.com/albums/ee153/theApocalyptican/100_0391.jpg

Page 60 of the Suburban catalog: Part 4 : Part # 32-0988 $22.95

[PJG1173]

Not to hijack this thread, but are those factory 4 tube radiators you guys are running or did you put them in... Mine has one but I got it out of a '76 and had to fab mounts for it... If they are factory what do the mounts look like?

they came factory in the BBC trucks so the mounts for a C/K 20 or 30 with a 454 should work. my buddy and I went through this when we put a BB in his 87 k5

[EagleMark]

Mine was factory. If you look them up on RockAuto you will find several differant size cores, the four core for towing option is of course the most expensive.

Lat year i had a little leak at a service valve and used my old R12 recovery machine so I could fix it. Well the machine had sprung a leak and I lost all my R12. I did not want to do an entire R134a retrofit as they really need a differant condesor, total flush of old oil, install new oil and it was middle of summer. So I tried that eviro stuff and it works even better then R12 and colder then this A/C ever was. Can contents say LPG... works with R12 oil R134a oil and can be mixed with both...

I've heard the rumors not to use propane but that is what they use in UK. Flash point for LPG is higher then R12 with oil... so I think it's all a big Dupont controvesy as the LPG works better then R12 and is OK in UK? Works great for me!

[TheApocalyptican]

I tossed around the propane idea, but just wasn't sure. Also didn't know where to get it with the right can tops/and didn't really wanna make an adapter. Think I had a small leak, but I tightened it up, and still is blowing cold, but it's not 100° yet. Was Enviro-Safe what you used?
Oh, and I also have a direct fit parallel flow condenser that works way better with the 134. I'm sure it would make any of the refrigerants work better.

[EagleMark]

Yup! That's the stuff and they have the can taps etc... I still use all same R12 fittings.

[dyeager535]

Just so you "big radiator" guys know, there are some significantly cheaper alternatives out there. http://www.championradiators.com/page/400669594

My Dad just bought the 3 row for his 454. We don't get nearly as hot out here as some do, but he does tow with it. The 4 row copper/brass replacements are ridiculously expensive from what we found.

Of course, that doesn't cover the "huge" radiator used with the diesels (and maybe some of the gassers later on), but from the picture TheApocalyptican posted, that's not what he is using.

Just thought I'd share that with you guys, in case you spring a leak and have to replace those 4 rows.

Me, I'm going to try and stuff an aluminum Corvette radiator in where the AC condenser used to sit. :)

[EagleMark]

Thanks I am do for a new one and would like to find a less expensive replacement, aluminum have been coming down over the years. Will have to check you link.

[TheApocalyptican]

I had a leak in mine, but had it repaired here in town. The rad "conversion" was partially done when I bought the truck. It had the OE rad fan shroud jury rigged, and the top supports were partially connected with wire. Finished the conversion, and had the rad completely cleaned and had the leak repaired for $105. I was looking at getting a nice aluminum one, but for $105, for what was essentially a new rad, I couldn't beat the price.

Also, don't know about the "huge" diesel rad, but I've yet to see a stock one bigger than mine(19 x 34 x 2.5). But if there is one bigger than mine.....it does have to be HUGE.

[EagleMark]

I got a tank starting to leak on mine, got all repair and maintenance records when I bought it and never saw a new one, so 22 years is pretty good! I like the 3 core aluminum one at that link for $209... I've heard they do as good as four core brass and are stronger?

[Xenon]

That looks like the same radiator I have... I just made mounts for the top - Took the stock ones and made them bigger so they would fit. Didn't know LMC had one...

[dyeager535]

I took a peek at my Dad's again, and while not impressed with the heater inlet, that can be worked around. It's threaded, and WAY too small ID. The mounts where the rubber its aren't quite the same as factory (not as defined due to the welds) but I think it's enough.

I don't know about stronger. I'm up in the air on that one. As bad as the C/K frames are (flimsy) I'd expect the radiator to take some twisting, but both the core support and radiator are rubber bushed, so that may not transmit to the radiator.