Automotive Air Conditioning Information Forum

Hi folks, I have a 71 Plymouth Scamp that was originally an AC car with slant six motor. The motor is now replaced with a 5.9 v8 from a 2000 Dodge Dakota. I want to use the more modern compressor and serpentine belt drive system on the 2000 motor.

I’m making all new hoses and plan to use a parallel flow condenser. I plan to reuse the underhood hard lines as well as the evaporator. Those will be thoroughly flushed, of course. Plus a new drier and expansion valve.

I plan to use the original refrigerant from 71. I have a lot of old cans of it laying around and I want the Scamp to be as cold as it was in 1971.

The compressor is new. I should replace the oil with mineral oil. Any idea how much? Also, any idea how much 1971 refrigerant I should use? The drier does have the glass viewport. Any other tips or special considerations for this build? Thanks in advance.

Back in the days when the Dakota used R-12 refrigerant (1993 and earlier), the specs I have for that vehicle are 40 ounces net weight (2.5 pounds) of R-12, and 7.5 fluid ounces of Mineral Oil. I don't have any specs for the 1971 Scamp with the Slant Six.

With that being said, I'm not an A/C system designer, and I can't say whether R-12 will work at all in a compressor designed specifically for R-134a (the 2000 Dakota). Typically, the process is reversed in that a system originally designed for R-12 (your '71 Scamp) is converted to R-134a, not vice versa.

GottaBeCold88 wrote: Wed Jun 24, 2026 11:29 am Hi folks, I have a 71 Plymouth Scamp that was originally an AC car with slant six motor. The motor is now replaced with a 5.9 v8 from a 2000 Dodge Dakota. I want to use the more modern compressor and serpentine belt drive system on the 2000 motor.

I’m making all new hoses and plan to use a parallel flow condenser. I plan to reuse the underhood hard lines as well as the evaporator. Those will be thoroughly flushed, of course. Plus a new drier and expansion valve.

I plan to use the original refrigerant from 71. I have a lot of old cans of it laying around and I want the Scamp to be as cold as it was in 1971.

The compressor is new. I should replace the oil with mineral oil. Any idea how much? Also, any idea how much 1971 refrigerant I should use? The drier does have the glass viewport. Any other tips or special considerations for this build? Thanks in advance.

You can get R134a as cold as R12 ever was fairly easily. The factory compressor on that 5.9L should be an ear mounted Sanden SD7H15. Sandens usually work with either refrigerant provided it has the correct oil. To me it would be far simpler to just run R134a. I have an 80s GM van that the custom system I built for it was reaching 16F from the center vent in 100F Texas heat and humidity last summer. That was not intentional, took me 3 different new low pressure cutout aka cycling switches to actually get one that was not defective. The first two failed in the on position and would not cycle at ~20 psi like they should have. My formula is simple, good compressor, largest parallel flow condenser that will fit, a clutch fan and shroud, and an electric pusher or two on the condenser if they will fit. Those Durangos had a 5 bladed and later a 7 or 9 bladed clutch fan. I would use the 9 blade fan if you can. Dorman repops the 9 blade for about $40. The 7 and later 9 bladed fans were V10 Ram fans and there was a TSB from Dodge to install them in place of the 5 bladed fans. The 9 blade fan overall makes less fan noise and kept both the engine and AC cooler. I have used the 9 bladed fan on a lot of Mopar stuff over the years from the Durango/Dakota to Rams and Ram Vans. One of my customers ~20 years ago was a airport shuttle service provider and he ran a bunch of the B350 vans. I could get those dual AC equipped vans ice cold with R134a and that 9 bladed fan on them. Those vans ran all day long and had a ton of idle time on them. Changing them from the 5 bladed stock fan to the 9 bladed unit dropped the AC pressures by a considerable amount and kept the engine and engine bay cooler, which helped the AC performance and compressor life. Another plus was the PCMs stopped failing when the engine bay was no longer scoarching hot.