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1979 Mark AC Questions & Update

Hey Bill,
I have a 79 Mark V and I need to work on my complete A/C system. All parts to the A/C are original to the car from what I know. It seems my evaporator sprung a leak and I had oil on the floor and my A/C stopped blowing cold. I figure now is the time to address any other potential problems and as I source parts I thought I would ask you a few questions.
I want to stick with R12 which I have 4 cans so far. I understand I need mineral oil but wasn’t sure if I need the cans that have 50/50 (R12/oil) or is the oil traditionally added separately when preparing a complete system. From what I understand, I need 68 oz of R12 and 10.5 oz of mineral oil. Is that correct? Since I don’t know how much oil is left in the system and it has been exposed to the elements should I perform a complete evac and start fresh?
I bought a new evaporator and drier. My compressor might have had a small leak although I have gone 6 years without needing a charge. There is oil on the hood insulation that was there when I bought the car. It could have come from a previous failure. The A/C was not working when I bought the car, but an A/C shop familiar with classic cars in Michigan tested, found nothing wrong with it. He did a complete evac filled it with R12 an it’s ran fine ever since. I was told these often seep oil especially if the pressure is too low in the system for an extended period. The mechanic thought this might be why the system appeared not to have any mechanical issues at the time. Can my compressor be tested or should I just have it remanufactured since this would be the time to do it OR is this the time to think about buying a new one considering its age? Is this a service Lincoln Land offers? What other items should I be looking at addressing at this time?
I was thinking of replacing the heater core if the A/C system is in the way of it’s removal since it’s original to the car though there is nothing wrong with it. Is the condenser also something I should look at replacing while I have the system apart? The hoses look good, but I’d like to find a way to test those also if possible.
Any input would be appreciated!
Thank you!
Happy New Year!
Brian –
Attempting to diagnose further problems into an a/c system that has performed well until a major failure of one component (evaporator) is foolish. If you absolutely must address and repair any unknown future “potential” problems, you will need to replace all of the parts that the refrigerant is routed through. Your mechanic gave you good advice in several areas, oil will migrate through the seal normally and slight oil streaking will appear on the hood insulation. Severe amounts of oil seepage are of course not allowed. Components of the system cannot be completely and accurately evaluated separately off the car at any repair shop level. This is performed at the manufacturing level. We evaluate and diagnose components while operating on the car. We also strongly recommend that faulty compressors be replaced with new and not rebuilt units for reliability and customer satisfaction purposes.
Do you have all of the necessary equipment to perform quality a/c repairs? Proper tools and equipment are a must along with the correct Shop Manual in order to sure of certain specifications and procedures. Good luck with your project.
I have the manuals and tools required and as for equipment, isn’t only a vacuum pump to evac and remove moisture needed and gauges to determine high/low pressure?
It seems everybody wants to retrofit the car and that’s something I really don’t want to do. I did that with another vintage car and was never happy with the results. People say you can’t get R12 anymore which is simply untrue. I have a supply and sources. I have a new evaporator and drier and currently looking for a reasonably priced NEW A6 compressor based on your advice. I do agree. Perhaps I will have the old one remanufactured and resold to save it from landfill and to offset costs.
Do you only retrofit vintage systems with R134a now at your facility or are you still working with original R12 systems at your client’s request? I have a very good mechanic but he doesn’t have a dedicated vacuum pump for R12 anymore and he is also suggesting I not deviate from R12 since he is familiar with the results of my last A/C retrofit of R134a in the other car.
Thank God it’s winter!!!
Thank you again!
Hi Brian –
In addition to replacing the faulty a/c parts and before evacuating we also pressure up the systems with nitrogen for a period of time and observe the gauges for a pressure drop in order to be certain that all leaks have been eliminated. Replacing the receiver/drier is a very good and recommended decision that you have made. The other luxury that successful a/c technicians develop over time is a keen feel for the system that they are working on. A feel for the system only comes with plenty of on scene experience and some unintentional ” trial and error”. Your local a/c mechanic friends may be able to observe your work and advise you further if necessary. I have worked with automotive a/c systems since the late 1960’s and still find that there is something new to be learned every day.
We at Lincoln Land are well aware of the shortcomings and disappointments of r134 in some of the older systems. R134 however does seem to work fine in certain older units and again not so well in others. The worst of r134 of course will mostly appear on the hottest of days and in slow traffic. We like to speak with our customers and let them make the refrigerant choice according to their desires. Most conversions that we perform receive (on our recommendation) the best equipment that we can source. We like to install r134 capable condensers and heavy duty cooling fans etc. according to the customers decisions. Many collector car owners are well aware that r134 may not cool as well as r12 and are quite happy with that while others do insist on the r12. In this business we must accommodate our customers accordingly as well as remain within the State refrigeration laws.

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