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Old 07-25-2010, 10:01 PM   #1
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trol a temp mastertrol. Thermostat cannot kick on blower and condenser

I have a old mastertrol MARK V (MABS V, made in 1984) for two zone heating and cooling. everything works fine for heating. But the thermostat on second zone does not call the cooling, the voltage between T4 and T5 (on mastertrol board) is 1.2V rather than 5V (whcih is measured on the first zone). jumper between T4 and T5 can kick on AC. but jumper between wire 4 and 5 on thermostat got no response. zone two got cold air when zone one is on. I have a AC contractor inspected it and he is confused about what he saw. It will be helpful if anyone can give me a hint about what is wrong.

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