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quivil 03-16-2012 05:41 PM

26VAC reaches heat exchanger...but...
Hey all,

I have a heat exchanger outside that is not working--no fan, nothing.

When I switch the thermostat to "AC" after a few moments the house fan goes on and at the same time I read 26VAC right at the heat exchanger outside--the same two wires that left the thermostat and arrive at the heat exchanger.

The thermostat signal is getting to the unit. I also read 240VAC on either side of a relay which is under the cover of the unit. I can see that this relay is not closing when the 26V signal arrives.

But the 26VAC does not go directly to the coils of the relay that starts the unit, there's something in between:

There's a device between the input 26VAC signal and the coil of the relay--it appears to be a heat sensing device because one side of it is attached to one of the condensing coils. One of the 26V wires goes through this device on the way to the relay coil.

As a troubleshooting question, can I run a jumper over this device long enough to see if the relay closes and the unit begins functioning? That would mean a bad...I'm assuming it's some sort of thermostat...device.

If that's not safe, any troubleshooting suggestions?


Edit: and by "safe" I do not mean safe to life and limb. I'm being very careful around the 240 Volts. I mean, is it safe on the hardware to do this test...

hvac5646 03-16-2012 05:57 PM

sound like a low pressure cut out. you could be low on gas. Pics would be helpful in this case.

REP 03-16-2012 07:42 PM

Don't understand.You say you have 26v to the contactor but don't know if the 26v are going through that device.
If you have voltage to the contactor and you have 240 volts to the contactor,then the contactor isn't pulling in.Its a bad contactor.
If the voltage stops at that device before it gets to the contactor then you have a differant problem and you have to figure out what that device is and what triggers it,I.E. would be low pressure ( low of freon).Then you have to fix that problem by finding the leak,fixing it then evacuating the system and refilling the system.Not a job for a home owner.

quivil 03-16-2012 08:14 PM

I agree
Now that the two of you have pointed out that the device I was speaking of is a low pressure switch, I agree, it's not a job for me!

Thanks much guys...


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