ACtion Magazine - March 2015 - (Page 22)

System charge determination By Ward Atkinson (Bill Hill, MACRAE LLC, contributed to this article.) C onversion vehicles which have additional cooling units added to the OEM's production front end A/C systems present a special challenge: establishing the "new" system's correct refrigerant and lubricant charge amounts. Modification of a Production A/C system with additional evaporator Vehicle manufacturers establish A/C system charges in an environmental test facility by running a charge determination test procedure at high ambient load conditions. from which the final charge amount can be determined. Then the vehicle is operated on the road (30 to 50 MPH under safe road conditions) at an ambient of at least 95 degrees F and as much humidity as possible. Instrumentation on the system requires high and low side system pressures, and tubing (pipe) surface temperatures at the compressor inlet and discharge lines, the TXV inlet line(s) and outlet air (panel and/or auxiliary evaporator) temperature. "T" into the low side pressure gauge line a charging hose attached to a small cylinder of refrigerant and an accurate measuring device. Since the original OEM front A/C system has an established charge Electronic scale Liquid amount, this amount of refrigerant can be used as the charge starting point in establishing the refrigerant charge curve. cylinder Operate so all system(s) have a maximum load (controls set to outside air, or vehicle windows open and high blower speed(s). Additional charge curves for various potential system operating modes should be established. To assure system operation when Environmental test facility Since companies in the conversion industry normally do not have access to a test chamber, there is a method (detailed below) that can provide some guidance by operating the modified vehicle under high load weather conditions to develop an on-road system refrigerant charge curve. Consideration for different system designs There is a large variety of A/C system designs used in today's vehicles. They can include systems with orifice tube expansion devices with low side accumulators, systems with thermal expansion devices, high side receivers (some with multiple receivers) systems. Others can have internal heat exchangers, systems with condensers that have built-in receivers and integrated sub-cooling loops, and systems which utilize both refrigerantto-water chillers as well as refrigerant-to-air evaporators. Some of these systems have very low refrigerant charges approaching 350 grams, and the amount of reserve charge that is designed into the system varies by vehicle manufacturer. This makes the conversion of an OEM production A/C system more complex. Some vehicle conversions also add an additional auxiliary condenser that will increase the amount of refrigerant required for operation. Establishing system charge The procedure begins with evacuating the system and installing a small amount of refrigerant as a starting point to develop a charge curve 22 ACTION * March 2015 Typical refrigerant charge curves

Table of Contents for the Digital Edition of ACtion Magazine - March 2015

Engine cooling systems: Electric cooling fan operating strategies
System Charge Determination
Service Port
Leonard's Law
Virtual View
Heavy duty and off road
Last Watch
Coolin Corner
Letters to the Editor
By the numbers
Industry News
Association News
In Memoriam
New Products

ACtion Magazine - March 2015