need a lesson in A/C

-
Johnny Mac

Johnny Mac

www.blueprintengines.com
FABO Vendor
Joined
Jul 10, 2010
Messages
4,343
Reaction score
4,841
Location
OHIO
So I have absolutely no experience with the older A/C systems and compressors, other than how to take them off of my core engines and take them to the scrap yard.

as some of you have seen, i picked up a 1978 dodge monaco with factory A/C. it appears to be in tact, but only blows hot. i haven't messed with it a ton...i really don't know what i'm looking for to see if it activates? and also if it needs recharged, if much goes into changing the freon? or converting it to the newer stuff, or if it's even worth messing with on this car. the only actuator valve i see actually looks more like a heater core blockoff?

part of me wants to yank all this garbage off of it, and the adult in me reminds myself how nice A/C would be if i can keep this a respectable driver, and have functioning A/C.

so any pointers would be appreciated. again it's a 1978. everything looks factory.
 

Attachments

  • imagejpeg_0_5.jpg
    52.7 KB · Views: 386
From what I've seen, converting to r134 with original equipment can suck, and no matter what you'll want to get a condensor designed for r134. Personally I wouldn't mess with trying to get it fixed and filled with freon.

I think Mancini and others sell a bracket to convert to a Sanden style compressor. I did this on my '79 C10 -

New compressor brackets
New Sanden style compressor
New custom lines, I cut the hoses, had a local shop crimp the fittings, and used a couple bend it yourself al. hard lines to make it all complete
New factory accumulator
New cross flow condensor

That's about it. Probably cost me around $600 and it blows ice cold. It does warm up a bit sitting still, thinking about adding an elec fan as a helper for heavy traffic, although I don't drive it THAT much so it's not a huge concern for me.

Bought a harbor freight vacuum pump and manifold gauge set, well worth it, I can now service my own AC systems and after a bit of reading it's not all that difficult.
 
Does the compressor clutch engage when the AC is turned on? That would be my first step.

If not, it probably is either very low or out of refrigerant. If it does, then it's likely you have a malfunctioning expansion valve, or perhaps one of the blend door vacuum servos is bad.
 
You could use a socket to turn the compressor by hand. Then if that seems ok. Crank it up, set controller for cold air, Use a carter pin to jump the wire connector removed from low pressure switch. If clutch engages, and compressor runs, don't run the compressor for a long time until you know the system is not low on Freon. If it is low on Freon, it got out somewhere. Dusty crud build up often tells the tale since some of the oil escapes too. Where you put that socket is a common place. That shaft seal can leak. owner would repeatedly add Freon. Oil loss causes a messy build up just above on the hood insulation.
 
If the compressor kicks in when jumping the low pressure switch than more than likely you have a leak in the system. You could pressurize the system with nitrogen to listen if you can hear it leaking. Or if you have a vacuum pump and AC gauges you can pull a vacuum and see if it holds overnight.
 
Thank you all. Will see if I can get the compressor to engage and see if I see any leaks. If the compressor kicks on, can I buy one of the do it yourself charge kits? Or will that stuff be bad news mixed with whatever is in it?
 
You cannot buy R12 anymore and that is what that system had or has in it, so it will have to be converted to R134a.

That will include and new drier at the very least. On systems that old, I always replaced the compressor and expansion valve, too. You will also need to replace every o ring in the system with R143a friendly o rings.

The system will need to be flushed thoroughly. I've always used a couple of cans of brake cleaner followed with compressed air until what comes out is clean and dry.

You will need to vacuum the system down good before you charge it. This gets all remaining moisture out.

The 134a charge is usually about 2/3 to 3/4 what the original R12 charge was. On a car with a pretty big passenger compartment like that, you can figure on somewhere "around" 36 ounces. It will end up being between two and three cans since they are 12 ounce cans now.

You cannot mix R12 and R143a together. You also cannot mix R12 oil and R134a together. This is why you must at the very least replace the drier, because the dried holds both moisture and a little oil.

This is also why I replace the compressor, especially on one that old. I have seen people remove the old compressor and "try" to drain the oil out, but it is nearly impossible and most times the old compressor will fail in a short time.
 
Well rusty, I greatly appreciate the lesson...I have to really ponder if I want to mess that much with it. Sounds like basically the entire system needs replaced beyond the hoses and brackets...probably more trouble than its worth. Thanks again.
 
I hesitate to "suggest" this but if you look around in "back alleys" R12 can still be had. I've got 20-30 lbs of it, myself. (I used to service HVAC/R)
 
I have 3-4 cans of R-12. But it's really not that hard to change to R134A. On my 69 Dart I flush the system with denatured alcohol. Installed a new dryer, drain my RV-2 compressor as best I could. Then I added 10 oz. of Ester oil which is the best oil to use when converting from R12 to R 134A, it mixes with any mineral oil that may be left in the system. Use a system vac pump to make sure it will hold a vacuum for 30 minutes. My Dart held 36oz. of R-12. When you use R 134A you use 80% of the R-12 amount, or in my case I charged it with 28 oz. It blows 36 degrees and the pressures were real good 35/225.
 
well if the compressor and/or clutch is shot, repairing it looks to get pretty expensive. This is looking like probably $400-600 that i probably don't need to spend on an $1800 car... the clutch alone is $70, the compressor is 150-200. She's adding up quick...but if the compressor and clutch seem to work, maybe i'll give it a shot. also reading alot of aftermarket intake manifolds don't clear A/C which would pose a problem for wanting a 4150 flange efi system
 
Regardless of what you do, IF you convert it to R134a, you must replace all of the o rings. The R12 o rings are not compatible with the R134a and it will be a short time before the system is leaking from every joint.

That in itself is reason enough "to me" to think about replacing major components, because you will have all of the connections loose.

Air conditioning is not "cheap" on anything. House, car, whatever. To me though, you have the whole system intact. It would certainly be nice to have it up and running, regardless of whether you convert it, or are able to find some R12.
 
RustyRatRod said:
Regardless of what you do, IF you convert it to R134a, you must replace all of the o rings. The R12 o rings are not compatible with the R134a and it will be a short time before the system is leaking from every joint.

That in itself is reason enough "to me" to think about replacing major components, because you will have all of the connections loose.

Air conditioning is not "cheap" on anything. House, car, whatever. To me though, you have the whole system intact. It would certainly be nice to have it up and running, regardless of whether you convert it, or are able to find some R12.
Click to expand...

agreed and thanks again. It'll really come down to what works and what doesn't. "in tact" is pretty relative because i'm still uncovering snipped wires and such from whatever hack job yanked off all the lean burn $hit. Also have a slow drain somewhere on the battery..so lord knows what i'm going to find.
 
If the compressor ends up bad, just buy it one piece at a time. It's not like we're going into the hot season. You got plenty of time. lol
 
I will tell you what I know about mobile a/c. Most people that work on cars do not understand how it works. If the system was made for R12 it will work much better with R12 in it, assuming it can be made to work. R12 is still available. Those old reciprocating compressors do not like R134a. Old hoses do not like R134a and they can leak badly. Condensers made for R12 do not generally remove enough heat when using R134a. Those cans or a/c fix you buy at the parts store do not contain R134a in general, since that requires a MACS license to purchase. Most parts store a/c fixit cans have a hydrocarbon compound in them, similar to propane. If you to have a shop to work on the a/c system, ask them if they have a micron gauge to use when evacuating the system. If they do, they probably know what they are doing.

I would consider this a all or nothing proposition. If anything needs to be replaced other than a drier, I would junk it all and convert the system to a full system with a Sanden compressor and R134a. Before doing anything I would fill the system with dry nitrogen to check for any gross leaks. If it passes, then vacuum the system, preferably under 50 microns but at least under 500 microns, and if it holds that for an hour it will hold refrigerant.

That's it. That's all I got. I might know more but I can't remember most of what I know, and half of what I can remember is wrong. #-o
 
Rustedwrench said:
I will tell you what I know about mobile a/c. Most people that work on cars do not understand how it works. If the system was made for R12 it will work much better with R12 in it, assuming it can be made to work. R12 is still available. Those old reciprocating compressors do not like R134a. Old hoses do not like R134a and they can leak badly. Condensers made for R12 do not generally remove enough heat when using R134a. Those cans or a/c fix you buy at the parts store do not contain R134a in general, since that requires a MACS license to purchase. Most parts store a/c fixit cans have a hydrocarbon compound in them, similar to propane. If you to have a shop to work on the a/c system, ask them if they have a micron gauge to use when evacuating the system. If they do, they probably know what they are doing.

I would consider this a all or nothing proposition. If anything needs to be replaced other than a drier, I would junk it all and convert the system to a full system with a Sanden compressor and R134a. Before doing anything I would fill the system with dry nitrogen to check for any gross leaks. If it passes, then vacuum the system, preferably under 50 microns but at least under 500 microns, and if it holds that for an hour it will hold refrigerant.

That's it. That's all I got. I might know more but I can't remember most of what I know, and half of what I can remember is wrong. #-o
Click to expand...

You need a 609 certification to buy R12 but can buy R-134A over the counter without certification. You can get a 609 certificate relatively easy and then legally buy R-12.

The "fix-it" kits widely available are known as " death Kits", they contain sealers that in some cases will totally wreck a system. There are two types of sealers used in these kits one is a relatively harmless O ring swelling compound. The second is a silicate formula the turns hard as a rock when exposed to air. This type can totally plug up your A/C system if things go wrong. These kits contain R-134A, not HC refrigerants. Cheap R-12 to R-134A conversion kits are also known as "death kits" because they generally dump in more oil to mix in with the old R-12 mineral oil. R-134A usually turns the old oil into some kind of sludge and the thinking is the new oil will then lubricate the compressor. Good A/C work requires the tools and knowledge of how these systems work. Cheap short cuts and " magic in the can" fixes usually don't end well.

As far as I'm concerned there are only three things you should put in an A/C system- pure R-12 or R-134a, the proper oil and a UV dye to help find leaks. I would never use a sealer of any type, fix the leak.
 
Pete in NH said:
As far as I'm concerned there are only three things you should put in an A/C system- pure R-12 or R-134a, the proper oil and a UV dye to help find leaks. I would never use a sealer of any type, fix the leak.
Click to expand...


You can preach it all day long, but some folks will not have any of it. I sell the stuff every single day at work. We have pamphlets on it that come out all the time to help warn customers about what works, what doesn't and what to stay away from.

IMHO, I don't think the auto parts stores should even sell refrigerants. People are "gonna do what they're gonna do" regardless of what they are told is right or wrong.

We get people on a very regular basis wanting "just the fittings" so that they can charge R134a right on top of R12. When you try to tell them not to do it, you get that deer in the headlight look.
 
Change to R-134A today? Don't you guys know it is outlawed in many countries and soon in the U.S.? I changed all my vehicles to Duracool, even my 2002 when the compressor failed. Works slightly better than R-12. But, if the EPA is watching, legally you must first convert to R-134A, even though that is very bad for the environment (climate change gas).

The only thing "old" about your design is the heavy compressor. Otherwise, nothing much has changed in AC, other than a parallel-flow condenser is 30% more efficient, but those existed in the 1960's. Your RV-2 compressor is very dependable, just a beast. For retrofit, a smaller Sanden is best choice, and you can get brackets for your SB (Bouchillon, etc). I wouldn't waste new refrigerant on those old hoses. If you have an AC crimper like me, it is easy, or buy Oeticker hose clamps on ebay and crimp w/ a nail puller, or even Breeze screw clamps work. Can also take to a hydraulic hose shop to refit.

If you don't have a good vacuum source, you can do "good enough" by sucking a vacuum w/ your intake manifold, switch to a hand vacuum pump and try to get it to at least 20" Hg, sit for hours to out-gas any water, fill w/ Duracool or Enviro-safe, then vent a little off to blow out any residual air or vapor. You can't legally vent hydrocarbon refrigerants per EPA, though that is what is in many hair-spray cans and cow farts. Also, first read the foolish worries about "explosive" HC refrigerant from non-tech people (zip it, I'm an engineer who studied combustion in grad school). No fires in millions of cars yet from that. If using R-134A, better to use PAO 68 oil since PAG absorbs moisture to form corrosive acids, in which case you better pull a very hard vacuum first.
 
Good gawd. I see CO2 is being listed as an "alternative." Do you folks HAVE ANY FREEKIN IDEA how high operating head pressures would be with CO2???????????????????????????
 
67Dart273 said:
Good gawd. I see CO2 is being listed as an "alternative." Do you folks HAVE ANY FREEKIN IDEA how high operating head pressures would be with CO2???????????????????????????
Click to expand...


I think it was the Germans who were looking into CO2 and yes the pressures would be ridiculous. As I recall the pressures were well over 1000 PSI. Given the high pressures required the idea didn't seem to go very far. I would imagine the costs involved to make it a safe system killed the idea.

It's the European Union who is really pushing to kill R-134A, although the phase out date in the US is supposed to be 2017. The replacement R-1234yf is slowly being phased in. It is supposed to be $60 to $70 a pound coming out of a joint venture Honeywell/ Dupont factory in China. As far as I know R-1234yf will not be available to us do-it-yourselfers.

Mercedes started using R-1234yf and then recalled 1500 cars and refitted them with R-134A citing safety issues with R-1234yf when it burns. The EU is in an uproar over that as R-134A is supposed to be illegal in the EU now.

We live in a very interesting world. I suspect when R-1234yf really hits the field R-134A will still be available but go to the R-1234yf price to keep people from converting back to R-134A when repairs are required.
 
RustyRatRod said:
If the compressor ends up bad, just buy it one piece at a time. It's not like we're going into the hot season. You got plenty of time. lol
Click to expand...

Ok...somewhat back on track. So I was able to hotwire the compressor, and it kicks on, but its not blowing what I would consider cold air. So that being said, the compressor is "good"? Probably just a leaky o ring?

So...guess I will keep it. Replace all the o-rings as you suggest. Flush the system. Replace the drier, and then find someone to fill it?as I imagine thats a one and done, and requires special tools?
 
johnnymac2k6 said:
Ok...somewhat back on track. So I was able to hotwire the compressor, and it kicks on, but its not blowing what I would consider cold air. So that being said, the compressor is "good"? Probably just a leaky o ring?

So...guess I will keep it. Replace all the o-rings as you suggest. Flush the system. Replace the drier, and then find someone to fill it?as I imagine thats a one and done, and requires special tools?
Click to expand...

If you are talking about filling it with R12, yes. That would work. That's what it sounds like has happened. The refrigerant has leaked out. You will need to find the leaks and repair them before you recharge it, though.
 
But I can't buy r12 correct? So im replacing all the rings with new ones, and finding a shop to fill it with whatever is legal this date in time.
 
Pete in NH said:
You need a 609 certification to buy R12. You can get a 609 certificate relatively easy and then legally buy R-12.
Click to expand...

Yep,
Just dusted off My Old MACS cert... dated '92, still valid :D & blew the dust of My Memory
CD... LOL

That being said, The RV'2's came in three (3) configs, uniquely categorized
by the 'oil pan' on the compressor bottom, no other changes.
1) Square, 4 oz 'sump'
2) Rounded corner, (driver side) 4.1 oz 'sump'
3) Middle deep--- 4 oz 'sump' .

All of the above 'pan' configs were modified simply for 'fitment',...
Ok enough of that.
P.s, there is a plug on the right lower RV2 housing
which when removed(0 vacuum,open system) allows 'oil' to be checked...
3" piece of Your favorite wire with an obligatory handle :D.
Checking oil condition may help with a $ decision.

I am just guessing (based on the limited pics) this is an "H" block "EPR" manual control
system, and as the compressor still 'works' when 'jumped',

I vote for this action Link

Me thinks You will be $$$ ahead from an 'alternate' refrigerant conversion...

With Respects, just borrowing a page from Mr Rob's--- GUIDE TO HOT ROD BLISS ---
 
You must log in or register to reply here.
-

Back
Top