Differences in early and late AC systems?

[TylerW]

Hey guys:

I wonder if someone could tell me if there are substantial differences in the early 70s factory air conditioning systems, and the system found on my '75.

My '75 has a different arrangement of lines and the receiver? mounted on the inner fender compared with earlier cars I've seen.

Thanks...

 

[67Dart273]

I guess I don't get what you are getting at. ALL refrigeration/ AC systems of the type in autos use the basic following setup:

The condenser in front of the radiator changes the hot gas from the compressor back to liquid and MAY act as a storage container

Many, probably most cars also have a tank AFTER the condenser known as a receiver. This is for liquid storage---most AC systems in homes just use the bottom of the condenser for this purpose

Next, the liquid--having been cooled by the condenser--goes to SOME SORT of metering device. This is the SECRET of all such AC units, and is exactly the same idea that happens when you use an air blow gun or air tool. You've noticed that when using air tools that they get COLDER as you use them. This is because the sudden drop in pressure out of an orifice causes WHAT IS KNOWN as "the refrigeration effect."

In the case of auto AC, you have the added cooling effect of NOT JUST a drop in gaseous pressure--as the example above of an air hose--but ALSO the EVAPORATION (boiling) of the refrigerant from liquid BACK TO a gaseous state

THESE TWO EVENTS--a sudden drop in pressure, and the boiling (evaporation) of the liquid refrigerant--causes a MASSIVE change in temperature, and is the very secret of the entire system.

NOW

This evaporating, boiling liquid gas/ mix is immediately dumped from the METERING DEVICE into the EVAPORATOR which is the indoor unit (house) or under-dash unit in your car

The airflow through the evaporator EXHANGES the heat in the cabin air INTO the cold evaporator AND CAUSES further evaporation/ boiling of the gas/ liquid as the heat is exhanged and transferred into the refrigerant.

NEXT the refrigerant MOSTLY gas, now, having absorbed the HEAT from the cabin, goes out of the evaporator AND BECAUSE it is now a gas, not a liquid, and HAS EXPANDED you ALWAYS have a LARGER DIAMETER tube/ hose coming OUT of the evaporator.

This large tube, known as the SUCTION or LOW PRESSURE side of the system, now feeds the refrigerant gas back to the COMPRESSOR which raises the pressure--and temperature--due to "heat of compression" and other losses (friction) in the compressor and sends this HOT GAS at high pressure known as the HIGH SIDE of the system out ALWAYS in the smaller sized tube/ hose BACK TO the

CONDENSER which does the OPPOSITE of the EVAPORATOR---the relatively low temperature air from the outdoors flowing through the fins of the CONDENSER now REMOVE heat from the condenser, and as the HOT GAS travels through the tubing bends of the condenser, this removal of heat eventually cools the hot gas back to a cooler LIQUID, and if used, this cooled liquid goes to the RECEIVER---and again we go round and round---headed right back to the EVAPORATOR

So to sum this up you have

Condenser----Receiver (if used)--metering device--evaporator--compressor--back to the Condenser

 

[TylerW]

...well...thank you for going to that trouble.

Let me attempt to clarify my question with a couple pictures:

The first photo is an early 70's A-body. Notice the receiver/dryer is at the far right front and the refrigerant lines appear to enter the condenser on opposite ends. This is the type I've seen up through 1973 or '74

The second photo is a 1975 Swinger. Notice that the receiver has been relocated to avoid the charcoal canister, and that both the lines reach the condenser from the passenger side.

My question is whether there are any significant changes in these two eras of AC systems or can parts be mixed and matched.

Thank you.

 

[RedFish]

Major changes occurred between 72 and 73 models both under the hood and inside the cabin. More insignificant changes such as what you've pointed out occurred between 74 and 75 models.

 

[yellowdartdave]

They also changed the firewall and the entry/exit points for the heater and A/C lines in 73.
Also, 73 only, the dryer was attached to the upper passenger side of the condenser.

 

[slantsixdan]

I wonder if someone could tell me if there are substantial differences in the early 70s factory air conditioning systems, and the system found on my '75.

Yes, there are. Almost every component is different. The in-car heater-A/C box behind the dash is different. The under-dash vent duct is different. None of them is bolt-in interchangeable with earlier parts. The underhood lines are different. The in-dash controls are different. The compressor's the same, but the '74-up A-body systems use an EPR (Evaporator Pressure Regulator) valve in the compressor's suction inlet to regulate evaporator temperature and a blended-air system to regulate air outlet temperature, while the '65-'72 system uses an adjustable clutch-cycling switch and the '73 system uses a nonadjustable clutch-cycling switch + blended air. Underhood pipeworks are different; the '75 system routes the suction and discharge lines the same direction coming off the compressor while the systems through '73 (maybe '74) route the suction line towards the passenger side and the discharge line towards the driver's side. Filter-dryer location differs as well.

It would probably be easier to retrofit a late A-body system in place of an earlier system on an A-body already equipped with factory A/C. It is an expensive, difficult, bloody nightmare to retrofit factory A/C to a car not originally so equipped—a mistake I made twice and will not make again. Upgrades are possible to the various systems, but that's not what you asked.

 

[yellowdartdave]

/6dan......
It is easy..........IF you have a complete same year A/C parts car sitting next to you and you are good with a plasma cutter, welder and other assorted tools. And a lot of patience.

 

[Charrlie_S]

Functionally they are the same. Mechanically they are different. Just like a 350 chevy and a 340 Mopar. They both use the same parts and accomplish the same thing. But you cannot interchage parts, between the two.

 

[TylerW]

Thanks guys...LOTS of excellent info.

The reason behind this question is that I have a complete AC system being removed from the soon to depart '75 Duster and the soon to arrive '73 Dart Sport appears to be missing everything ahead of the firewall.

 

[SirDan]

Also if you swap a 70-72 front end onto a 73 (-76?) car there plug on the receiver/dryer thing slightly interferes with the front end. but you could fix that issue with some small cutting.