Differences between 1979 ac unit and 1982-86

[V679]

Hi everyone, I have a 1979 coupe with factory ac. I wanted to replace the ac system with a system from a 1982-86 and would like to know what the differences are between the 2. There are conversion kits that convert to r-134 for 1982-86 Mustangs but none for 1979-81. So I wanted to know if anyone knows what is different between 1979-81 and 82-86 ac systems. My biggest concern is the heater/ac box and if I would need to change this for the ac lines to connect to it. If anyone has done this or has any information regarding the conversion or interchangeablility between 79-81 and 82-86 ac systems please let me know what you know about them. Thank you

[V679]

I also have one other question. Would the ac lines from a 1987-93 connect to a 1979 ac/heater box? Specifically where they meet at the firewall. Thanks again.

[erratic50]

When you use R12 /R134a compatible oils you should be able to simply verify there are no leaks, evac the system, and go for it.

[V679]

That's great news. Tank you

[V679]

Thank you

[vintageracer]

I suggest you change ALL the "O" rings in the system before your refrigerant conversion.

R12 cars typically have the old black "O" rings in the system that are now 37 years old. Replace ALL of the black "O" rings with new green colored R134 compatible "O" rings, replace the Drier, evacuate the system, charge it with R134 & correct oil and "Dollars to Donuts" you will have "Chilly Wind"!

[wraithracing]

The are several differences between the 79 A/C OEM units and the later model. The biggest is the early cars use an H valve rather than the orifice tube that the later models use. The hole in the firewall is completely different also. I converted my 79 PC from no A/C to the 83-86 style unit and had to cut the firewall hole for the Evaporator core tubes and the heater core tubes to go thru. Bottom line is not a task I would want to do with the engine in the car IMHO. A lot of the wiring for the HVAC system is different between the early years and the later model years too. The compressor, the brackets, etc are all different too.

The evaporator core is generally broken down into the 82-86 models and the 87-93 models. The real difference is the orifice line on the 82-86 is threaded where the 87-93 uses a spring lock connector. Obviously the lines match up by years also with the biggest difference being the 83-85 Carburetor Discharge hose and the 86-93 EFI Discharge hoses being totally different. Condenser is same 82-93.

Bottom line is if you have a complete donor system from a later model Mustang, then the swap might be worth the trouble IMHO. Otherwise have your original system repaired as needed by a competent A/C shop. If that is not an option you might consider looking at an aftermarket A/C system such as Vintage Air, Old Air Products, Restomod Air, Classic Auto Air, etc. as one those systems will most likely be a cheaper option and honestly work better than a hodge/podge of OEM parts.

In my experience the OEM Mustang HVAC system when converted to 134a only works moderately well at best. Most of my experience was around Austin TX with typical high humidity and high summer temperatures, but needless to say I wasn't impressed. I know others feel differently, but I will never make the conversion again. I will only use R12 in the OEM HVAC. I will say the Hoze Wizard conversion kit does work pretty well when installed properly, but it still doesn't compare to the OEM HVAC with R12. Best of Luck!

[erratic50]

Doing a standard evac and charge I will agree the R12 systems converted to R134a are sometimes lackluster. It depends a lot on how well it's done. The condition of the compressor, clutch, and pressure switch make a huge difference. Also cars with underdrive pulleys tend to have marginal AC.

When I was a young boy the oldtimers I was around (my grandpa and his friends, etc) who were in their 80's at the time talked about how refrigeration evacuation is a bit of a load of crap because there is still air in there. They talked about the original methods used on the very early refrigeration units worked better. Those had a larger moisture trap in them and had done to them what those old guys referred to as a "displacement evacuation".

Not sure that's really a thing but that's what they called it.

Rather than trying to suck all the air out they would replace it by leaving the compressor off and holding the high side open while shooting refrigerant in the low side until it streamed out the high side. The theory was that then a much larger percentage of the air was pushed out. Once that's done you charge like normal and go off pressures to determine if it's full.

Having personally converted both an 86 and an 89 this way and having fixed a few R12's traditionally my opinion is that after verifying the condition of everything else was up to par the function of an R134a with traditional evac vs displacement is night and day. The R134a displacement evac systems worked every bit as well as the R12 system worked when new, if not better. On a hot summer day at 110 degrees outside the AC on max would blow 42 degrees on the 89 and 45 on the 86- quite acceptable in both cases imo.

cant speak to the work to swap setups across years, etc.

[V679]

Thank you for all the info. Put lightly darn. Was hoping for a realitively easy swap. I will look for a good ac shop in the area.
I was planning to swap a 1988 302. Do you know if the brackets from a V6 will with the accessory brackets from the 88 302. Thanks again for all the help. It really is appreciated.

[JACook]

The Nippondenso 6P148 compressor used on the '88 is a far better piece than the York unit your car came
with. It can work just fine with the '79 system, you'll just need to find a shop that has the capability to make
up the lines for you.

Expansion-valve type systems (what yours is) are not nearly as friendly for refrigerant swaps than the later
orifice tube systems. This is primarily because expansion valve systems need to have the same kind of gas
in the expansion valve sensing tube, as what's running in the system. Secondarily, most expansion valve
automotive systems did not come with generously-sized/highly efficient condensers.

But given the existing stocks of R12 are currently larger than the demand, the only good reason to retrofit
is if you can't find a shop that held on to their R12 equipment, though it's questionable how good a reason
that is...

Also, if the only way you judge the success of an R134a conversion is the vent temps, that's rather a 'what
I don't know can't hurt me' approach. If you don't know how high the head pressures have gone, you don't
know how successful the retrofit was.