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    yxue's Avatar
    yxue Posts: 2, Reputation: 1
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    #1

    Apr 25, 2008, 04:08 PM
    Inside A/C air blower won't start
    Hi,
    I have a heating and cooling system in my condo. The heating is working fine, but the A/C does not. When the room temperature is above the set temperature, the outside A/C system (compressor) kicks in and the inside evaporator coil becomes cold, but the air blower simply won't comes up whether the Fan switch is on Auto to On. The thermostat is Totaline P374-200. I did some diagnosis, and here is what I found
    - If I connect R and W using a jumper, heating system will start and so does the air blower (so I can say the air blower is working)
    - If I conned R and Y, the A/C system kicks in (I can hear the freon circulating) and the compressor and its fun running, and the coil becomes cold, but the air blower won't start
    - If I connect R and G, the air blower does not start either.

    My guess is the fan relay switch is not working. Am I right? But why it works when in heating mode. Do heating and cooling work the same way and use the same relay switch?

    Appreciate any expert advice.

    Thanks
    T-Top's Avatar
    T-Top Posts: 1,871, Reputation: 100
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    #2

    Apr 25, 2008, 08:35 PM
    Do you have a gas furnace or heat pump? If you have a heat pump and jump R to W the heat sequencer will control the blower on a older gas furnace the A fan/limit switch will control it in heat.How old is the system and what brand is it?
    yxue's Avatar
    yxue Posts: 2, Reputation: 1
    New Member
    		  
    #3

    Apr 27, 2008, 08:20 PM
    I have a gas furnace for heating. Both Gas heating anf A/C systems are one year old in a brand new condo. The A/C system has a out-unit (compressor) from U.S. A/C Products and it's not clear who manufactured the in-door fan coil unit. The heating coil is using heated water from the gas furnace.

    My biggest question is why the blower can start by jumpping R and, not R and G or R and Y.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #4

    Apr 27, 2008, 09:26 PM
    In most systems in heat mode, the furnace controls the fan. This is necessary for a few reasons: 1) So you don't get a blast of cold air AND 2) So that the fan runs for a short time after the burners shut down do that you extract heat from the plenum.

    The device that helps do this is the fan limit control. e.g. http://customer.honeywell.com/TechLi...0s/60-2259.pdf

    In COOL mode, the thermostat controls the Fan. Thus in cool mode, the t-sat makes a connection from R to (G and Y).

    Another thing that usually happens is that cool may use higher speed than heat.
    acetc's Avatar
    acetc Posts: 1,004, Reputation: 79
    Ultra Member
    		  
    #5

    Apr 29, 2008, 08:24 PM
    Sounds like you have a faulty fan relay, if you go to the furnace and check the voltage at the coil terminels on the relay while it is calling for cool, you should read 24 volts if not then you may not be getting a signal from the thermostat indicating a faulty thermostat. Good luck, Mike
    hvacservicetech_07's Avatar
    hvacservicetech_07 Posts: 1,083, Reputation: 75
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    #6

    Apr 29, 2008, 08:43 PM
    I'd say you have a relay problem, most likely a circuit board, if you have already touched R&G together at the t-stat, and the fan doesn't come on. Check all of your low voltage connections at the furnace, try jumping R & G at the circuit board terminals.
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