How to service A/C?

[3175375]

I agree with #John Kirby and others, you will be much better off doing an underhood conversion to R134A including new Sanden compressor and modern condenser. I did a LOT of research and did this successfully on my 66 wagon with dual A/C and it still works after two Texas summers. Here is my thread, check it out.

66 Monaco Wagon A/C Resurrection

I agree that the condenser needs to be replaced if converting to R-134a, if you want decent performance.
In my mind, all new vehicles with R-134a are undersized to minimize the reduction of fuel economy.
If you can get the R-12 system to work properly, it will cause your testicles to retract...

 

[John Kirby]

I agree that the condenser needs to be replaced if converting to R-134a, if you want decent performance.
In my mind, all new vehicles with R-134a are undersized to minimize the reduction of fuel economy.
If you can get the R-12 system to work properly, it will cause your testicles to retract...

True, but getting it to work will cause your wallet to constrict like you've never experienced. And it's the compressor that needs replacing, not the condenser. The only reason I mentioned replacing the condenser is the vast majority have been beaten on for over 50 years and the fins don't let much air through anymore.

 

[3175375]

True, but getting it to work will cause your wallet to constrict like you've never experienced. And it's the compressor that needs replacing, not the condenser. The only reason I mentioned replacing the condenser is the vast majority have been beaten on for over 50 years and the fins don't let much air through anymore.

I agree with you that the compressor is likely to be replaceable, as the condenser. However, my point is that due to the characteristics of R-134a, a larger condenser is required than what R-12 needs. So, even if the R-12 condenser is good, you’re degraded out of the gate if you don’t replace it.

 

[ayilar]

@71Polara383 has replaced the worn A/C components on Medina, my 1971 T-code Monaco. Now it is time for charging, but Wyatt does not have the equipment or gas. The specialist in Lake Zurich whom we had planned to do the work told me last week that he was booked solid through July, so we decided to go local.

My local classic-car mechanic has the equipment and R12 needed to test the vacuum and to charge the system. I just need to know the charge weight and pressures to shoot for when the system is running. Thoughts? @saforwardlook @413 @3175375

 

[413]

Service manual has all of this info. The pressures are VERY dependent on outside temperature. There is a chart in the service manual.

 

[3175375]

This: Determining the Refrigerant Capacity of a 1974 Dodge Charger SE | Classic Auto Air - Air Conditioning & Heating for 70’s & Older Cars & Trucks.

your system may need more or less. the factory service manual should specify.

 

[TxDon]

This: Determining the Refrigerant Capacity of a 1974 Dodge Charger SE | Classic Auto Air - Air Conditioning & Heating for 70’s & Older Cars & Trucks.

your system may need more or less. the factory service manual should specify.

The majority of the research I did when I converted my system said that the best way to charge with R134 is by pressure rather than weight or quantity. The correct pressures vary depending on ambient temperatures when charging. If you are going to do a complete conversion yourself you will need to buy or borrow a good set of gauges and charge hoses plus a vacuum pump.

 

[saforwardlook]

The only thing I can add is that vacuum testing the system is a pretty good way to check for leaks but it isn't always fool proof since the actual system operates under pressure. So if you do detect some leak or loss of cooling over a relatively short period of time, you might want to inquire whether your local tech has refrigerant recovery equipment for R12 so you don't lose all of that expensive R12 in case something does leak under pressure but didn't show up under the vacuum test. Sometimes a new part in the system such as an expansion valve or pressure control switch in the backside of the compressor doesn't work properly, so again to replace such a part, you would want to recover the freon since the system will have to be opened up again to fix the issue. I learned that the hard way once..................

 

[EurekaSevven]

If your system has no charge and you know that to be the case use a dye and UV to attempt to locate it - probably by unscrewing one of the lines to the condenser and squirting some in there while engine is sitting (since the system isn't running while sitting and therefore the refrigerant finds the lowest points in the system, usually the evaporator if memory serves).

Amount of freon depends on your car, but assuming this is the stock RV2, I think the spec was around 3lb 2 oz to 3lb 6 oz. Don't top it off because that decreases cooling, the principle is that your evap coil inside your cabin sucks up your humidity, which requires space in the refrigerant - this is accomplished by low pressure with the proper charge.

And I actually have R12, I got it from eBay - the law is 'supposed' to require you to have EPA 609, but when I got it eBay never asked me.

Speaking on the stock A/C compressor, I was talking to CBODY67 about it in DMs and he brought up that it was possible to adjust a screw on the EPR valve by a 0.05 turn, decreasing the vacuum pressure, therefore making it compatible for R134a. Raised my interest greatly, since R134a is far more available than R12.

 

[3175375]

Agreed that pressure is used for R-134a. However, he’s talking about R-12.
Additionally, R-12 is WAY MORE FORGIVING regarding charge, whereas R-134a has a very narrow ‘sweet spot’.

 

[EurekaSevven]

The spec I was referring to was from the FSM, which is for R12 - which probably explains the range of 4 ounces for charge being acceptable, compared to what r134a would be in this case. My point was more that topping it off is bad regardless.
In this case I would probably do around 3 lb 4 oz and see how it does, if it can be done better I would drain some out (you're supposed to reclaim it because of EPA laws, but I used to work at an HVAC place and we never did that).

 

[EurekaSevven]

Although I just now realized this is a 71 Monaco and not a 68 Chrysler, which is where I got that from - I...don't think there would be a difference in charge? Even for R12 - I would look at that @ayilar. As far as my educated guess goes it'd be the exact same system but there might be a few differences, I'm not actually sure.

 

[ayilar]

Thank you all ( @EurekaSevven @3175375 @saforwardlook @TxDon @413 ) for the rapid and helpful responses. Couple of comments to follow up:

1. The compressor's silver tag lists the pressure -- 3lbs 6 oz is what it says. Note that this compressor came from a 1971 Polara but is not the original -- the latter was found last year (by he specialist in Lake Zurich) to work but leak in a manner that was not fixable. The rest of the system seemed good, including all the new parts I'd bought and that Wyatt had installed last year.

2. My plan is therefore to ask my local classic car mechanic to draw a vacuum on the system before anything. Spin the compressor clutch by hand to be sure the seal is good. Then he can recharge.

Put differently, because of what we learned from the LZ AC shop last year, our only concern this time around is the compressor. The new one pictured above is the last one Wyatt and I had on hand that seemed to be in working condition. I hope it is.

Thoughts?

 

[saforwardlook]

Thank you all ( @EurekaSevven @3175375 @saforwardlook @TxDon @413 ) for the rapid and helpful responses. Couple of comments to follow up:

1. The compressor's silver tag lists the pressure -- 3lbs 6 oz is what it says. Note that this compressor came from a 1971 Polara but is not the original -- the latter was found last year (by he specialist in Lake Zurich) to work but leak in a manner that was not fixable. The rest of the system seemed good, including all the new parts I'd bought and that Wyatt had installed last year.

View attachment 469994

2. My plan is therefore to ask my local classic car mechanic to draw a vacuum on the system before anything. Spin the compressor clutch by hand to be sure the seal is good. Then he can recharge.

Put differently, because of what we learned from the LZ AC shop last year, our only concern this time around is the compressor. The new one pictured above is the last one Wyatt and I had on hand that seemed to be in working condition. I hope it is.

Thoughts?

I believe a good used compressor is likely the best way to go these days when a new seal is put in. I have heard nothing but bad stories about using rebuilt compressors - they never seem to go the distance, especially when using R134 refrigerant.

One other way to tell when the system is getting near full is to watch the sight glass on the receiver dryer for the bubbles to just go away and then stop the charging and also to monitor the discharge temperature out the vents for maxing out in terms of lowest temperature achieved.

Good luck on the efforts!

 

[3175375]

The compressor that you have on hand will work fine, if it doesn’t leak. Capacity-wise, I have followed the advice previously posted. The first thing to do, is to make sure that your system can hold a vacuum. The seal on that compressor might need to be replaced, and a vacuum test where you pull a vacuum and have it hold overnight or longer is the first step. Once you get that done, then you can put in a charge of R-12. You should see results after about 1-1/2 to 2 pounds of refrigerant. For R-12, the site glass is a valuable way to indicate how your system's performing.

Air conditioning register temperature is also another helpful metric to use for determining the best performance, but it usually follows how full or clear the site glass is as well.

regarding the data plate and it’s stating 3.6 pounds of refrigerant, whether it was from a Monaco, 300, imperial, fury or anything else except a station wagon with rear air, 3+ pounds will be damn close. Remember, or 12 is very forgiving and you got a lot of slop in the amount of charge to get to the best performance point.

I installed in R-12 aftermarket system (all 65-66 Mustangs came with an under dash evaporator) in my 1965 Mustang and it calls for 1.75 pounds of R-12. After putting in one 12 ounce can of R-12, it started performing well and I continued to charge it until the site glass cleared up. At that point, the register temperature was near freezing (32 degrees F).

Another teaching point regarding R-134a is indeed that refrigerant is better measured by high and low side pressures, driven by the outside air temperature. I have used the chart below for Mel, the 1995 Buick Roadmaster recently and nailed the charge using it.

go and do the work and report back!

 

[413]

Change the oil in the compressor. It gets dirty and gets moisture in it. The type of oil is different for R12 and R134. You can get the oil and a new gasket for the compressor oil pan at the AC parts store also. To determine full level the service manual shows you how to make a dipstick to put in the fill hole and measure the level.

 

[ayilar]

Thanks guys for the advice. I am happy to report that the system holds a vacuum -- here are the readings yesterday at 11AM when the test was started, 3 hours later, and just now.

Last year, with the original A/C compressor, the Lake Zurich specialist showed @71Polara383 that he had the vacuum drawn and it was holding (good) BUT when he turned the AC clutch by hand, Wyatt could hear it start leaking (bad) -- he turned it some more and the leak stopped. He recommended to replace the compressor, which we did thanks to a donor car. For this reason, Wyatt recommended that, with the new compressor in place, my local technician turn the A/C clutch by hand and see if it makes a difference. Happy to report that there is none, so it looks that I am all set. Charging will start soon.

 

[70bigblockdodge]

Still waiting for the 134 to leak out of the original hoses so I can change the Schrader valve that leaks and is capped by a old original brass cap.
Don't believe the hype. Re-o ring the system flush and fill with proper oil and add new valve and dryer. Done

 

[3175375]

Still waiting for the 134 to leak out of the original hoses so I can change the Schrader valve that leaks and is capped by a old original brass cap.
Don't believe the hype. Re-o ring the system flush and fill with proper oil and add new valve and dryer. Done

That sounds good! However, the system will underperform with the R-12 condenser. It may not even be noticeable, except in high outdoor temperatures…

 

[david hill]

Thanks guys for the advice. I am happy to report that the system holds a vacuum -- here are the readings yesterday at 11AM when the test was started, 3 hours later, and just now.

View attachment 471453

View attachment 471454

View attachment 471455

Last year, with the original A/C compressor, the Lake Zurich specialist showed @71Polara383 that he had the vacuum drawn and it was holding (good) BUT when he turned the AC clutch by hand, Wyatt could hear it start leaking (bad) -- he turned it some more and the leak stopped. He recommended to replace the compressor, which we did thanks to a donor car. For this reason, Wyatt recommended that, with the new compressor in place, my local technician turn the A/C clutch by hand and see if it makes schader difference. Happy to report that there is none, so it looks that I am all set. Charging will start soon.

Replace the Schrader Valve cores to prevent future leaks.