AC fixed w/ ACC - might help you - PeachParts Mercedes-Benz Forum

BillGrissom · #1 04-18-2014, 05:23 PM

1984 300D w/ factory AC compressor (Harrison R4). When bought, it had R-134A adapter fittings (no sticker). AC belt broke a few years ago when my son was driving home from San Diego on a hot August day (probably >105 F). Fortunately, just a few miles from our house since the AC belt apparently tangled in the p.s. belt, flipping it, which let it "chainsaw" a hole in an oil cooler hose, spraying oil under-hood. I got around to fixing the AC this winter.

I had assumed the AC compressor seized (common), but found it spun freely, so decided to try it. I even bought a new R4 compressor on ebay cheap ($100), but changing one is tedious. My 1985 300D smoked the AC clutch on a hot day a few years before, though that compressor also spins free. I have another R4 that came on a used 1981 engine now in my 1985. Thus, I have incentive for an R4 solution. I did convert my 1985 to a Sanden (Rollguy's bracket) so my son won't have issues far from home.

Another data point, is that the AC compressor in my 2002 T&C smoked the AC clutch (common) on a 108 F day last year. I had just added a can of R-134A since the low-side was running 22 psig. I must have pushed it over the limit. R-134A produces higher pressures, especially in our hot Central Valley. My 1985 had R-12 when it smoked, as I recall, but perhaps I over-filled it. My suspicion is that some R4's aren't seizing, they are just slipping a clutch or belt from too much refrigerant pressure.

Pushing on, I changed the 1984 to Duracool hydro-carbon refrigerant, which has worked well for me in other cars (in my 1985) and added ~6 oz of their new oil (PAO 68) since it mixes fine with the R-134A and PAG oil which was probably in the system. After two 6 oz Duracool cans, the pressures were right (~25 psi low, ~100 psi high), the suction tube and evaporator were cold, so the AC system was working fine. However, no cold air was coming out the vents. The heater core is bypassed (fixing a leak), so wasn't a hot water controls issue.

I figured the problem was a climate door control issue. I read that in AC mode the center vents should be blow, and they weren't. I swapped the push-button box w/ a spare, but no help. I took the box apart and it looked fine inside, w/ no cracked solder joints. I cleaned the relay contacts, though they looked new. I later opened the junkyard box and it looked OK but worse (darker copper). I removed the Temperaturreguler box (behind glove box) and found the circuit board looked pristine. I thought of changing the capacitors since they can degrade over time, but too much work. I put it back in the car, tested, and got cold air from the center vents (plus side vents). Don't know how I fixed it. The connectors were tight, but sometimes removing and re-inserting cleans pins (also used contact cleaner). Maybe the box relies on a ground thru the attachment screw and re-installing cleaned that. There was no visible corrosion (this is CA).

Take-away for others. Don't give up on your R4. Read up on PAO 68 oil (Duracool calls it Ice something). It is supposed to stay in the compressor much better and doesn't absorb moisture. Taking a box in and out can sometimes fix things. I am looking forward to a cool summer on the upcoming > 110 F days here. And less pressure to smoke the clutch or belt using Duracool.

BillGrissom · #2 09-01-2014, 05:02 PM

Update. I drove the 1984 300D home from San Diego yesterday (left son the 1985). It was 99F outside as we started the I-5 climb out of the LA Basin. We sat in a >1 hr traffic jam before Lake Hughes Rd (mini-SUV driver died after slamming into trailer on shoulder). The AC blew cool, but couldn't keep up with the afternoon sun with the car barely moving. I could hear the electric radiator fan running. It was slightly better with the windows down, since we at least got a breeze. Once we started moving, the AC blew cold again.

I haven't checked refrigerant pressures yet, but I suspect a generic issue with the AC design. It simply can't manage our high ambient temperatures. The Sanden compressor in the 1985 300D doesn't seem to do much better when stopped. The problem appears to be that the outflow from the condenser gets too hot when stopped (almost too hot to touch). Perhaps a new parallel-flow condenser is the only solution.

leathermang · #3 09-01-2014, 05:33 PM

First , Hydro carbon refrigerants are ILLEGAL in moving vehicles in many states.

Second, Duracool is a BLEND.... thus... if you have a small leak the smaller molecules leave first..( and there is a very small one built into the R4 to lube the front seal ) then you CAN NOT just top it off..
you have to evacuate it and refill with the blend to have the same characteristics.

Almost no shop will deal with you if you have anything other than R12 or R134a... they have to keep their machines clean and certified...... so if you get caught on a trip or can't address the AC for some reason.... you have a problem.

The idea of filling a system without using gauges is really bad.
You either need a really accurate scale... AND you need to know how much your system needs to work correctly... under filling is much much better than overfilling..
any change... like a P flow condenser changes the total amount your system needs.
In the old days many used the ' site glass' to fill ... filling until there were no bubbles showing..
The Mercedes AC FSM specifically warns against that... as there are conditions which will show bubbles even when the system is FULL...
We have had several people in the past... Red Fox I think was one of them .. Diesel Giant another... who SOLD Duracool and posted lots of things of dubious value... always leaving off the downsides....

AS to the strength of the R4 compressor and the higher pressures which R134a run.... in the archives is my post about what the AC pros in San Antonio told me when I mentioned the same thing... they said that you had to look for the correct serial number.. as the R4 was being used on all sorts of current vehicles WITH R134a with NO PROBLEM....

BillGrissom · #4 09-01-2014, 05:57 PM

Duracool (and other HC refrigerants) is legal in CA. Laws outlawing it in a few states were mostly pushed by AC shops who want to limit consumer choice. It has been used in millions of cars for decades with no report of causing a fire. For fun, I once tested it when I caught some liquid while venting some. You could light the liquid pool (on concrete), but it burned very weakly. I would be much more afraid of carrying a newspaper in the car.

I always use gages when adding refrigerant. My comment was simply that I have not checked the pressures after noticing the AC weak yesterday when caught in a long traffic jam. I may not bother now since Fall is approaching. I have no concerns about dealing with AC shops. I can do it all myself. I have an MS in ME and no need to bow to mechanics or listen to their often strange understandings of thermodynamics and heat transfer.

R-134A works OK and is fine for most regions of the country. Where I live, ambient temperatures can hit >110F causing high-side pressure w/ R-134A to approach 300 psig vs 250 psig w/ R-12. That can cause the AC clutch to slip w/ fatal results. HC refrigerants run slightly less pressure than R-12 (for same cooling effect). I wouldn't use R-134A in any retrofit today because it is soon to be outlawed. I use PAO 68 oil with any refrigerant today because it works better and doesn't absorb moisture and form corrosive acids like PAG oil does, plus works for any specified viscosity.

funola · #5 09-01-2014, 06:06 PM

Hey Bill, of the refrigerants R12, R134 , Duracool and ES12A, which has the smallest molecules? I have a stash of ES12A and may put that in my 85 300D once I figure out what's wrong with the Klima relay.

BillGrissom · #6 09-01-2014, 06:22 PM

I don't know molecule sizes. I assume the question regards leakage rates, since smaller molecules leak faster (helium even leaks thru thin metal walls). I would guess that R-134A is bigger since I recall the liquid is denser, though can't directly compare liquid to gas densities. I think ES12A (Enviro-Safe) is about the same as Duracool. It use to have a different brand name. Both are mostly propane, with other hydrocarbons.

I understand that HC refrigerants are used in home refrigerators in Europe. In the U.S., the EPA has long unofficially opposed it for unknown and perhaps strange reasons. They mention unknown personnel safety concerns, yet safety is not their mandate. Read the info on their website and decide for yourself if any of their non-explanations make sense. One oddity is that they require that you first convert to R-134A before converting to HC. A direct R-12 to HC conversion is not legal. Feel real guilty if you do that at home. And don't vent any R-134A because it is a potent greenhouse gas, which is the new environmental threat. Seems the "ozone hole" (reason R-12 was outlawed) was always there and not man-made, best I can figure, and the "deformed frogs in Costa Rica" wasn't due to increased uV light, but rather a bacteria that has been there since the dinosaurs. But research for yourself.

vstech · #7 09-01-2014, 06:45 PM

Ain't it funny that the ozone hole is no longer the evil threat it used to be? Now it's carbon footprint and greenhouse gasses... but ALL the refrigerant issues crop up after the patents expires from dupont. ..

leathermang · #8 09-01-2014, 07:11 PM

Detailed Questions About HC-12a ®, OZ-12 ®, DURACOOL 12a ®, EC-12a, and other Flammable Hydrocarbon Refrigerants | Alternatives / SNAP | US EPA

SD Blue · #9 09-01-2014, 09:29 PM

Aside from how much stock you put into the EPA and their "opinions", it sounds like the trouble with such high ambient temps is getting enough air flow across the condenser.

I've always wondered if another option might be a misting system to help out when the ambient temps get into the Sahara range. If it used a temp sensor and pulsed, it might make the water last longer.

BillGrissom · #10 09-03-2014, 04:56 PM

Quote:

Originally Posted by SD Blue

... it sounds like the trouble with such high ambient temps is getting enough air flow across the condenser. ...

I agree. My problem of "not cool enough at idle" is independent of refrigerant. Earlier I found the temperature of the liquid tube by the filter/drier was almost too hot to touch when idling and the air tepid from the vents. That was in my other 300D w/ Sanden compressor. I manually actuated the fan (jumpered 30 to 87 in relay base) and it greatly cooled, as did the air from the vents.

I suspect the problem is that the temp switch on the filter/drier is set too high. RollGuy has a post showing how to wire the fan relay so it blows anytime the compressor is on. This is a good kludge, especially if you mostly drive in the city. However, on the highway you shouldn't need the fan, so it would waste energy and wear out your fan. I think I will start looking for a different temperature switch. It doesn't penetrate the pressure boundary (just a mechanical screw attach), so easy to change.

vstech · #11 09-03-2014, 06:37 PM

The issue with high ambient is twofold: first, there is less heat transfer from the compressed gas to condense enough liquid to adequately cool the cabin... Second, the higher sensible and latent heat IN the cabin forces too much gas to the compressor, making additional heat that needs removal... Catch22...
A solution would be to lower the blower speed to lessen the heat influx to the evaporator, which would cut down gas pressure, allowing the condenser to at least function...
Adding additional condenser space, and a bigger accumulator would help also.

Tmadia · #12 09-05-2014, 12:30 PM

If you find a suitable lower temp switch please let us know. I would definitely be interested in that as well.

leathermang · #13 09-05-2014, 02:02 PM

Quote:

Originally Posted by SD Blue

...... the EPA and their "opinions",

it sounds like the trouble with such high ambient temps is getting enough air flow across the condenser. ......

!. the EPA can enforce it's " opinions " with big fines... and even if that does not affect a person's actions... it can affect the shops with which some might need to deal.

2. Air Flow across the condenser is the bottle neck of any AC system... so perhaps a good cleaning... make sure all the fins are straight ... in the condenser AND the radiator... since the air has to go on past the condenser ... and a HIGH efficiency fan might be the first , logical, and cheapest major improvement in the situation.

tjts1 · #14 09-05-2014, 02:24 PM

Quote:

Originally Posted by leathermang

Detailed Questions About HC-12a ®, OZ-12 ®, DURACOOL 12a ®, EC-12a, and other Flammable Hydrocarbon Refrigerants | Alternatives / SNAP | US EPA

Quote:

In certain circumstances, the replacement of HFC-134a in a motor vehicle with hydrocarbon refrigerants might be permitted. At a minimum, in order to avoid violating the Clean Air Act, the motor vehicle A/C system must have either been originally designed for use with HFC-134a refrigerant, or must have been previously retrofitted from CFC-12 to HFC-134a refrigerant, AND no sham retrofit must have occurred to convert the system to the hydrocarbon refrigerant. In order to avoid violating other laws, the replacement of the refrigerant must not violate any state or local prohibition on the use of flammable refrigerants in motor vehicle A/C systems.

The following 19 states ban the use of flammable refrigerants such as HC-12a® and DURACOOL 12a® in motor vehicle air conditioning, regardless of the original refrigerant: Arkansas, Arizona, Connecticut, Florida, Idaho, Indiana, Iowa, Kansas, Louisiana, Maryland, Nebraska, North Dakota, Oklahoma, Texas, Utah, Virginia, Wisconsin, Washington, and the District of Columbia.

Well that answers, that. End of story.

BillGrissom · #15 09-15-2014, 03:15 PM

Quote:

Originally Posted by tjts1

End of story.

Sort of not. Many people question how "flammable" is defined. R-134A also burns, and it produces poisonous phosgene gas as a product, which was used in WWI. Even R-12 burns. Stay away from the tail-pipe of a running engine after an accident in case the AC condenser is venting and getting sucked thru the engine.