Thermostat

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SERVICE MANUAL 12VDC WALL THERMOSTAT AIR CONDITIONING SYSTEMS ROOFTOP UNITS ONLY ! WARNING - SHOCK HAZARD!
TO PREVENT THE POSSIBILITY OF SEVERE PERSONAL INJURY, DEATH, OR EQUIPMENT DAMAGE DUE TO ELECTRICAL SHOCK, ALWAYS BE SURE THE POWER SUPPLY TO THE APPLIANCE IS DISCONNECTED BEFORE DOING ANY WORK ON THE APPLIANCE. THIS CAN NORMALLY BE ACCOMPLISHED BY SWITCHING THE BREAKER FOR THE AIR CONDITIONER TO OFF, DISCONNECTING ALL EXTERNAL ELECTRICAL CONNECTIONS AND CORDS, SWITCHING ON BOARD ELECTRICAL GENERATORS AND INVERTERS TO OFF, AND REMOVING THE CABLE FROM EACH POSITIVE TERMINAL ON ALL STORAGE AND STARTING BATTERIES.

DANGER
SOME DIAGNOSTIC TESTING MAY BE DONE ON ENERGIZED CIRCUITS. ELECTRICAL SHOCK CAN OCCUR IF NOT TESTED PROPERLY. TESTING TO BE DONE BY QUALIFIED TECHNICIANS ONLY The steps outlined in this manual are intended to guide the service technician through the process of correctly diagnosing a Coleman Mach series rooftop air conditioner with a remote wall thermostat control system. Page -1-

TABLE OF CONTENTS

PAGE I. II INTRODUCTION TO WALL THERMOSTATS ...................... 3

INTRODUCTION TO RELAYS ................................................. 5 HOW DO RELAYS FUNCTION ..................................... 5 CHECKING CEILING PLENUMS WITH INDIVIDUAL RELAYS ...................................................................................... 6 CHECKING CEILING PLENUMS WITH PRINTED CIRCUIT BOARDS .................................................................... 8 CHECKING THE THERMOSTAT OPERATION .......... 9 CHECKING THE PRINTED CIRCUIT BOARD OPERATION .................................................................. 10 DIAGNOSTIC FLOW CHARTS ............................................... 11

III

IV

V VI

WIRING DIAGRAMS ............................................................. 16

Page -2-

I. INTRODUCTION TO WALL THERMOSTATS All of the air conditioning functions are controlled by the wall mounted thermostat . These thermostats utilize a 12 VDC electrical circuit which is supplied by the vehicle manufacture or the installer of the A/C unit. Most of the thermostats provided by Recreation Vehicle Products are combination (Heat / Cool) thermostats. These thermostats are capable of operating both the roof top air conditioner and any furnace with a 12 VDC control circuit. The Figures below list three of the most commonly found Coleman/RV Products Wall Mounted Thermostats for rooftop air conditioners (heat pumps excluded). These thermostats are listed in chronological order from the oldest to the newest. 1. Mechanical / By-Metal Thermostats Heating Anticipator

2.Electronic Thermostats

3.Electronic Digital Display Thermostats

NOTE: ALL THREE OF THESE THERMOSTATS ARE COMPLETELY INTERCHANGEABLE. Thermostats are really nothing more than temperature controlled switches. When the need for Cooling or Heating exists the thermostat sends a 12VDC(+) signal to the control relays or a P.C. board which in turn energizes the air conditioner components or the furnace. (Note: Relays and P.C. boards will be further discussed later in lesson II). Page -3-

The following chart shows the different electrical connections made by the thermostat during operation. The chart below assumes12VDC(+) is supplied to thermostat Red wire “R” and that 12VDC(-) or ground is supplied to the Blue wire “B” at all times. Thermostat Operations Cool Mode Selected On Low Fan Cool Mode Selected On High Fan Heat Mode Selected On Any Fan Speed (Note: Furnace blower operates independently from sequencer or time delay in furnace) Fan Only Selected (Hi-Fan Only) Internal 12VDC(+) Connections Made Red “R” to Yellow “Y” and Gray “GL” Red “R” to Yellow “Y” and Green “GH” Red “R” to White “W” Red “R” to Green “GH”

Note: When the auto cool mode is selected on the thermostat the fan cycles “on” and “off” with the compressor as needed. When the on cool mode has been selected the fan runs continuously and the compressor...
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