Aw, man—you did it. Served me up a subject that I half-way understand and want to share. Those conversant with and knowledgeable with pumps, compressors, condensers, evaporators & etc. may wish to delete or switch channels.
Too tempting for this old ME to not try to pass on information that might help other better understand the pumps, compressors and fluids in their Chrysler 300’s.
Regarding selection of hydraulic fluids: Power steering service and power top service (and, in days of yore—power window service) are not particularly demanding with regards pressure or temperature levels. Selection of a brake fluid needs to consider all the materials in the system and the likely minimum and maximum service temperature. Can’t have the stuff boiling, corroding or breaking down from the heat of the brake system. So, a less complex fluid will suffice for a power top or power steering pump, provided the fluid will stay fluid at sub-zero temperatures.
Secondary effects, including potential for staining or damaging the paint or fabric on our brutes, are noteworthy. Finally, the great unknown—what will be the effect on the (probably old) seals in the pump and hydraulic cylinders. Cost of fluid for these small systems should not be a factor but they would probably run just fine on 10W non-detergent motor oil. I’d bet power steering fluid is not much more than that. The markup on a pint of power steering fluid must be tremendous.
Segue: Above, we were discussing pumps. The term pump is usually applied to a device that converts low pressure liquid to a high pressure. That is the device we use to pressurize liquids. There are exceptions such as a vacuum pump which pumps low pressure gas to higher atmospheric pressure. We call the device we use to inflate tires a tire pump. So, some compressors are commonly called pumps. Some call that 331 Cid to 413 CID device under the hood of our brutes a motor, but it is an engine and we engineers must tolerate common usage and not criticize it.
Anyway, that largest belt-driven device with the interesting plumbing under the hood of your brute is a compressor. It compresses low-pressure refrigerant vapor (gas) to a vapor at higher pressure and higher temperature. This hot refrigerant vapor then passes through that big black heat exchanger (technically, a condenser) in front of your radiator (which is actually a convector—but that’s another misnomer and story) where it exits at slightly lower pressure and considerably lower temperature, having been cooled by outside airflow. The refrigerant is now near the high discharge pressure of the pump and the lower (somewhat above outside ambient air) temperature refrigerant becomes a warm liquid-still at high pressure. The liquid refrigerant then flows through the dryer/receiver where any contaminants such as scale or water vapor are trapped. This round device should always be warm to the touch. The refrigerant is plumbed to near the heat-exchanger coil (technically, an evaporator) in the air box of said Chrysler 300 where it passes through a device (called an expansion valve, or more commonly in automotive service, a section of mall-diameter tubing called an orifice tube that quickly and efficiently lowers the pressure of the liquid refrigerant before it passes into the heat exchanger in the air box. The refrigerant is now very cold due to the rapid expansion (lowering of pressure) and may be a mix of very cold liquid and gaseous refrigerant. Hot, humid air from outside of your 300, (or from near the floorboard inside the car if your HVAC system is on MAX COOL or recirculation) now is passed over the outside of the coils, causing any remaining liquid refrigerant to evaporate “boil” (hence the name of the heat exchanger in your air box is the evaporator—it’s OK to call it the air conditioner coil) into refrigerant vapor.
If all is well, the cooled air will exit the vents in the 40-45-degree F range and the warmed/evaporated refrigerant vapor will enter the suction side of the compressor. Simultaneously, much of the water vapor in the hot, humid air of your 300 will condense on the outside of the evaporator coil and must be drained out of the car. This drain must be kept open to keep condensed water vapor from flooding the air box and your nice carpet. Further, a balance of refrigerant and air flow is necessary to avoid the condensed water on the coil from freezing solid on the outside of the coils, blocking air and greatly reducing the temperature reduction of the circulating air.
Not to complicate things too much, but on some cars, the air conditioning compressor is also actuated during the defrost process. This removes most of the water vapor from the circulating air before it is directed to the inside of the windshield. Opening the heater control valve to reheat the defroster air before it renters the defroster ducts helps melt the fog or ice that may condense and form on the inside of the window. Ice on the inside of all car windows from your hot breath happens a lot north of the Mason-Dixon line. If you don’t reheat the defrost air in Houston, atmospheric moisture will form on the outside of the windshield, causing a need for windshield wipers on cool and foggy morn.
Engineers and technicians struggle mightily to design the components of the air conditioning system to work over a wide range of temperatures and humidity’s as well as when the car is stopped and idling or motating down the road north of 100 MPH. And, with one to nine+ passengers. Even in the best of systems, don’t expect 40-degree air at the vents under all conditions. A lot of testing goes on to get maximum customer satisfaction. Add-on systems would be even harder to tune.
We've heard this before about brake fluid.
Anybody know why brake fluid would be manufacturer used over hydraulic oil. Brake fluid seems just plain dumb for all kinds of reasons, not the least of which is that it is hygroscopic for heaven's sake - duh... But we are not engineers. What do you engineers say?
Since it is available, today we guess that one should use top of the line true synthetic hydraulic oil but which brand and exactly which Spec.? On expensive to fix cars, people today are using more and more Red Line, Royal Purple, Amsoil and the like.
We are interested in reading what knowledgeable others have to say.
Sooo what should we do and why?
Posted by: "Rich Barber" <c300@xxxxxxx>
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