air conditioning

This is a long post. I cant remember where he said it, but I’m almost positive he claimed to get 47* air vent temperatures. Please remark on any and all errors
I think he knows what he’s talking about because almost all new cars come with r134a and some of them are COLD!
runinwthedevil said:
Joe,

The key to any successful A/C system function, (particularly in the case of a rotary compressor system like Dodge's), is a clean system. Unfortunately for most of us the days of the old, highly efficient R2 compressor, R-12 systems are all but gone.

The entire system must be power flushed, (professionally preferred), and absolutely devoid of contaminants and sediment, whether from a previously failed compressor or just years of use. This is a must.
Not unlike any other petroleum / non-petroleum lubricating oil, compressor oil eventually breaks down and gums up components whose proper function is essential to the system's highest performance resulting, obviously, in the coldest possible air.

Most 134A changeover kits now recommend not flushing the system, as this breaks loose trapped residues and particles that may be more detrimental to the "new" system, than good. Additionally, since most ester oils are now compatible with previous R-12 system oils, theoretically it's no longer required to rid the system of any remnants of the R-12. It should be at the individual’s discretion, (knowing the history of the system; i.e.; prior failures, known leaks, dryer and expansion valve replacement history etc.); as to what degree of system cleaning is acceptable. Let's just say, the cleaner the better. At the same time all o-rings and seals compatible with the ester type oil should be replaced too.

134A is a "larger" molecularly configured substance, or denser in composition, therefore less of it is required to create the same cooling effect as R-12. Note: Typically, 85% of the original R-12 system required capacity is all that is required to achieve the same cooling. This is particularly important, because I have found in the changeovers I've performed, that the amount of ester oil, (system specified quantity), to the 85% 134A ratio, is a very sensitive aspect of the changeover. This can often be the single difference that makes a R-134 system performance acceptable or totally unacceptable.

Secondly, in an R-12 system, where lesser degrees of condenser cooling is available, (due to a body lift installation for example which makes less of the condenser available to air flow), the R-12 system performance losses are negligible, and may even go unnoticed. However, in a 134A system this loss can be a large contributor to poorer performance.

Additional considerations for whether you have a chance of optimum 134 A system performance would be: Is the clutch controlled cooling fan function acceptable? (This should always be checked.) Has the original fan drive pulley been altered in diameter? Is the fan shroud installed to maximize air draw across the condenser, radiator etc? Does the fan sit deep enough in the shroud? If a body lift has been installed, have all the resultant "air leaks" been appropriately plugged? Was the radiator / shroud repositioned to keep the fan in the center of the shroud? What kind of shape is the radiator in? Is a factory or an aftermarket trans cooler installed forward of the condenser further restricting airflow to the condenser?

My point here is that every aspect of the cooling system function must absolutely be maximized to make a 134 system perform acceptably.

In either case, whether starting from scratch due to a catastrophic failure or simply changing over because of 134A cost and availability, a new expansion valve should be installed. Additionally, the dryer should be replaced, and proper handling observed prior to installation, (i.e.; capped so as not to saturate the desiccant with moisture from the air.)

Ensure that the capillary sense tube and sensor are properly mated. Typically, I withdraw about an inch and a half of it out. This allows the compressor to cycle longer because it takes a cooler temperature at the cap tube to cool it, because more of it is exposed to the warm air.
My truck is a '90 318 ci; 518 auto o/d R/C. Typical of all Dodge trucks, it had the factory single coolant line heater control valve. While this helps keep the heater core cooler initially, (in the A/C mode), eventually through thermal transfer of the coolant in the other hose, the core reaches overall cooling system operating temperature. To remedy this, and further improve my cold air output temp, I installed a '90 Dodge Daytona Turbo Z heater control valve. When in the A/C mode, vacuum is sent to the valve and closes the coolant flow circuit off from the heater core completely. It actually creates a "U-turn" for the coolant between the intake manifold and the water pump. Think of the heat that you're eliminating from the plenum area in the truck where you're trying to flow cold air.

Another thing I did, was to make sure all vacuum servos were operating efficiently and plenum or air box doors were in the proper position, and sealing like they did from the factory when in the A/C mode. Also clean all debris from the evaporator area. Mine was probably 65 - 70% restricted with leaves and crud.

Something I stumbled onto after my own conversion, (because yes, I too was less than satisfied initially), was that after operating the A/C for about 15 -20 minutes, (engine operating temperature achieved), my A/C compressor started cycling on and off. I performed all the high and low-pressure side checks, checked the low-pressure switch for operation and all electrical connections. What I found was that the "A/C Cutout Relay", (located on the driver's side of the fender), would heat up. When it did, the coil inside didn't have enough power to keep the points engaged causing the A/C clutch to disengage. When the coil cooled, the clutch engaged. When it heated up again, the compressor would disengage, minimizing compressor run time.

All of the scenarios I've mentioned are all obviously less detracting from R-12's highly effective ability to cool. Enough said.

I know this has been a wordy expose on optimizing the operation of a 134A system, but these are the kind of things that must be done to get it to work acceptably. Most of these things are almost always disregarded by the mechanically inclined "do-it yourselfer". No one will ever be happy with 134A performance unless you're willing to do what I have discussed. Hope this helps other readers. I merely learned by doing like we all do.


Dave Randall,
(a.k.a. [email protected])