GMW15775

Description / Abstract: Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. Determine if the control of the compressor (clutch control, variable displacement mechanism, or compressor speed) adequately protects the system from condensate freeze. An evaporator core freeze result in reduced compressor oil circulation and can result in compressor damage. Customer comfort will be reduced when airflow is reduced by icing. A secondary purpose of this test is to demonstrate refrigerant superheat control under prescribed of conditions. This procedure has the required instrumentation and test sequence for a subcool and superheat analysis without additional testing.

Note: The refrigerant charge variation included in this test is not sufficient to evaluate condensate freeze below Operational refrigerant charge. (i.e., GMW15775 is not a low refrigerant charge evaluation test).

Note: A change in the refrigerant used in a vehicle HVAC system has a significant impact on system performance and will require revalidation of evaporator freeze testing. A change to the Thermal Expansion Valve can impact condensate freeze performance and require an audit of the identified worst case conditions.

Applicability. This test procedure is for use on a full vehicle in a climate wind tunnel.

Remarks. This test procedure is to collect data during Heating Ventilation and Air Conditioning (HVAC) system validation.

GMW15775 is a vehicle-level test to perform final system verification of evaporator condensate freeze with production intent designs, controller, software and calibrations under a set of vehicle operating conditions. Steady state velocity conditions do not exercise Proportional, Integral and Differential (PID) compressor control logic used in variable displacement (pneumatic, electrically controlled, and electrically driven variable) Compressor Control systems. The GMW17775 vehicle speed profile or alternately the protocol from 4.3.2.3.4 assess the risk of dynamic evaporator local icing.

GMW16571 shall be used as a test technique to determine the optimal location of the refrigerant control sensors (Evaporator Air or Fin Temperatures, refrigerant temperature probes or refrigerant pressure transducers).

GMW16571 shall be used to develop initial calibrations with a proposed sensor placement and production intent control design that will provide robust protection from evaporator condensate.

Note: Engineering consideration should be applied where the production intent control points vary with ambient temperature. The matrix included in this procedure does not comprehend the impact of variable control points in terms of the effective evaporator loading and in regards to determining worst case frosting conditions. Using a fixed control point regarding ambient change during system frost control development may enable a more robust frost control data collection for the initial evaluation of the 12 test points.