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1985 Mustang GT, 5.0L, 5 speed
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Discussion Starter · #1 ·
I just bought a 1985 Mustang GT, 5.0, manual. It did not come with factory AC (and has no A/C presently). I'm looking at putting AC into the car because and I'm not about toughing it out these summers in a black car in Florida.

My rough plan was to grab all the brackets, hoses, and everything from a parts car from a salvage yard. I already have this just about figured out and I think I know where to source these items from. Then I'd probably go pick up a LMR kit to convert all that R12 junk to R134A and would give me some newer components that I hopefully wont have to worry about for awhile. All the under the hood stuff I'm feeling pretty good about doing and sourcing.

My questions come down to, I've only pulled a heater core / dash out once, like 15 years ago and I'm feeling rusty about it. I don't know the nuances of what is under the dash in the car I have and I don't want to figure it out when I get there. I'm hoping someone can answer for me, for a non a/c car of this specific year, does the under dash air handler come standard with both heat and a/c, with just the a/c elements missing out of it? Or is it a totally different air handler box depending if you had a/c or not?

If needed, can I swap in any fox air handler that has a/c or do I need a 85/86 specific since the dash is different than the newer foxes?
 

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1985 Mustang GT, 5.0L, 5 speed
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Discussion Starter · #3 ·
Sheesh this is really looking like a project. Just amassing resources in one thread as I go.

 

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Totally different air handler box from non a/c car compared to a/c car. I know that 85-93 a/c equipped air handler boxes are the same. But unsure about earlier cars. But yes you would have to modify firewall as well. Daunting task there.
 

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1985 Mustang GT, 5.0L, 5 speed
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Discussion Starter · #5 ·
But yes you would have to modify firewall as well. Daunting task there.
Yea, definitely much more work than just replacing some parts. I may have to think hard about this.

I know that 85-93 a/c equipped air handler boxes are the same.
At least for finding parts this simplifies things a little bit.
 

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You sure it’s 85-93 and not 87-93? I seem to remember the heater cores on the non-ac 85/86 cars were different and could be swapped out just by flipping the glovebox down. I think the ac units were the same as 87+
Yes the non a/c 83-86 are different air handler boxes and yes way easier to change the heater core because they were right behind the glove box. But the factory a/c equipped cars air handler boxes were the same from 85-93.
 

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Try Vintage Air. They make some trick systems for older cars. The heat and AC are incorporated into one unit that they supply. Hopefully there's an option for your car.
 

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The fittings on the evaporator are different from 86 to 87, so you'll need an 87+ evap with the correct lines to make it simpler, plus the correct lowside pressure cutoff switch for 134a vs R12.

The firewalls are the same - there is a blank cover over the air box closing off the evap line openings. There sometimes is a difference in compressors on factory AC cars vs dealer installed AC. The stock Denso compressor isn't really good for 134a as its lubrication sump tends to allow the oil charge to pool excessively at its lower piston bore, plus the original R12 condensor tends to have the same problem with oil settling, since 134a doesn't dissolve oil like R12 does.

You're better off with the Sanden compressor if you can find a kit with it instead of the Denso. Its much more efficient with 134a and keeps the high side from running away in pressure from 134a having the tendency of operating under super heat condition in an R12 fox AC system.

Original Air sells a kit - part number 23-106 with a modern style rotary compressor and it uses the stock style Denso mounting brackets, so you'll also need the factory serpentine bracket from an 86+ fox. Makes sure to use the correct viscosity and quantity of oil the new compressor calls for.
 

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I have a factory-air 86 GT. In my experience, the part most difficult to get is the dash mounted HVAC control box. Mine broke after all these years of use and finding a stock replacement was near impossible. And the air/non-air cars are different. Be very careful messing with that box - it's all plastic in the back.
 

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plus the original R12 condensor tends to have the same problem with oil settling,
Since he's going all new, he should be fine as all the modern offerings or the foxbody are the flat tube parallel condenser, similar to what came on the Sn95 mustang with R134a. Outside of NOS, i don't think you can even get the serpentine style condenser for the fox anymore.

These newer condensers are a smaller internal volume than the older serpentine condenser so your oil/refrigerant charge needs to be reduced. Original spec was 10 oz of oil and 40 oz of R12, up until 1989 when the oil was reduced to 8oz. When i redid my system (brand new, from scratch) I was advised to try a 34oz charge (i used R12) and 8 oz of oil in the system since I changed to the newer style condenser. I did, and the system works beautifully.
 

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The fittings on the evaporator are different from 86 to 87, so you'll need an 87+ evap with the correct lines to make it simpler, plus the correct lowside pressure cutoff switch
I forgot about those fittings being different on the evaporator good call. Anyway going about this is going to be difficult unfortunately. The A/C control box the vacuum tubes behind the dash all the above mentioned is going to be a nightmare.
 
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