Ac controls: dometic comfort control center

What it is

The Duo-Therm/Dometic Comfort Control Center (CCC) is a 12V wall thermostat that talks to an AC power module (control box) in each rooftop or basement unit over a 4-conductor phone-style cable. The power module has the relays, DIP switches and plugs. It can run up to 4 zones from one thermostat.

NEVER mix 4-button circuit boards/CCCs with 5-button circuit boards/CCCs.

No display

12V at the control box: 10 to 16 VDC between the red (+) and black (-) leads. Outside that range = erratic operation. None = supply breaker or fuse.

12V at the wall jack: plug the cable into the AC module RJ-11 jack, read red to black at the thermostat end. None = cable.

The 3 amp fuse is the only replaceable part on the power module.

Then do a system reset.

System reset (5-button CCC)

1. Turn the ON/OFF switch OFF. 2. Hold MODE and ZONE together while turning the switch ON. 3. 'FF' shows until you release MODE and ZONE. Required any time a DIP switch is changed after first setup.

CCC2 (newer): with the thermostat OFF (blank or clock only), hold MODE and ZONE. The LCD shows 'IniT' and the zones found. Release, then press ON/OFF to exit.

The cable

Must be 26 gauge stranded copper, 4 conductors (yellow, green, red, black), RJ-11 4-position plugs. Black wire on your LEFT looking at the top of the plug. Do NOT use a pre-made phone extension: its pin order is reversed and it will cause a system failure.

Test the module outputs (rooftop AC, 6-pin plug)

Disconnect the unit and use a 115V light bulb from terminal 5 (white, common) to each terminal. The bulb lights = the module is closing that circuit. Do not use a voltmeter here; it gives false readings.

TERMINAL 1 (BLUE)|Compressor

TERMINAL 2 (BLACK)|High speed fan

TERMINAL 3 (YELLOW)|Medium fan (AC) / reversing valve (heat pump, cool mode only)

TERMINAL 4 (RED)|Low speed fan

TERMINAL 6 (GRN/YEL)|Chassis ground

If the circuit is completed to a component and that component still won't run, the problem is in the rooftop unit, not the thermostat.

Fan runs, no compressor

Load-management: the two yellow leads on the control box. If they touch each other or are shorted through the metal box, the compressor will not run.

PTCR: clamp the start-cap wire. At start you should see current for about one second. None or a long reading = bad PTCR.

Cold control (freeze sensor) in the evaporator coil, plugged into blue P5. When the coil reaches freezing the compressor stops and the fan goes to high.

Capacitors: discharge first (15,000 ohm 2 W resistor). Bulged/split = bad. Ohms to the case = bad. Meter should swing toward zero and back. Caps with a 15,000 ohm bleeder: check on the 1,000 ohm scale.

AC voltage must stay between 103.5 and 126.5 VAC.

Sensor ohms (Dometic CCC sensors, ±10%)

55°F|11,667 Ω

60°F|10,212 Ω

65°F|8,959 Ω

70°F|7,876 Ω

75°F|6,939 Ω

80°F|6,126 Ω

85°F|5,418 Ω

90°F|4,802 Ω

95°F|4,264 Ω

100°F|3,793 Ω

Heat pump ambient sensor (red P3) adds: 25°F 27,271; 30°F 23,528; 35°F 20,348; 40°F 17,642; 45°F 15,334; 50°F 13,360 ohms. Heat pumps run down to 30°F. Remote sensor plugs into white P4.

Coleman-Mach (Airxcel) freeze and room sensors are a different part: 10,000 ohms at 77°F (25°C), about 12,492 at 68°F and 8,057 at 86°F. Never use a sensor from a different control system.

Remote sensor placement

54 in. above the floor, on an inside partition (never an outside wall), away from doors, windows and supply registers, with good air movement. Not in corners or under cupboards.

DOMETIC|Dometic Bulletin A29/2A, Troubleshooting the 5 Button Comfort Control Center System, Form 3307835.003 (via myrvworks.com, OCR)

DOMETIC|CCC2 Diagnostic Mode With Reset quick reference (via myrvworks.com)

COLEMAN|Coleman/Airxcel ohm values for freeze switch and room sensors (via myrvworks.com)