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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Carrier Weather Maker (10+ years old) and Rodgers

Customer Question

Hi , I have a Carrier Weather Maker (10+ years old) and White Rodgers 1F95-1277 thermostat that have worked well together for years. Last week the fan and compressor won't come on. Air handler blows if fan is on or when calling for cooling. Contactor points weren't very good looking but fan came on when manually pushed. I replaced the contactor anyway and also the capacitor, which was measuring a little low (36.5) on the HERM side. Reset the thermostat too. Although I have to pull the thermostat off the wall to check, everything is measuring about 27 VAC there. The wires from therm to air handler and air handler to compressor meet at the edge of a circuit board, but don't pass through it - no signs of a fuse either. When the thermostat calls for cooling R-G and R-Y at the air handler measure close to 0, while they are at 27 VAC at the thermostat wall mount. My next guess is thermostat, but it seems working. Any ideas, and thanks!
Submitted: 8 months ago.
Category: HVAC
Customer: replied 8 months ago.
Also, drain pan at water handler is bone dry.
Expert:  airheatman replied 8 months ago.

Check between Y and C and G and C at air handler instead of R and Y and R and G.

You will get any reading between R and G or R and Y as they are the same "leg" so to speak.Thermostat is like a light switch breaking the R leg from transformer to all components.

WE will go from there.

Customer: replied 8 months ago.
Thanks for the quick answer. When cooling is off Y-C is .21 VAC and G-C is 27.8 VAC. When thermostat calls for cool Y-C and G-C are both about 27.75 VAC. When thermostat is pulled off wall while in cool mode both Y-C and G-C drop to near 0.
Expert:  airheatman replied 8 months ago.

OK sounds like thermostat is doing its job. We just are not getting the voltage outside or we have a high voltage issue. Go to outdoor unit and remove service panel. Check for the 27.5 volts at contactor coil while thermostat is calling for COOL.

http://i.imgur.com/eRgWiMO.png

If we have the 27 volts at contactor coil and plunger is pulled down, check high voltage in and out of contactor.

http://i.imgur.com/pT2mWjq.png

We can go from here.

Customer: replied 8 months ago.
Thanks for the quick answer. When cooling is off Y-C is .21 VAC and G-C is 27.8 VAC. When thermostat calls for cool Y-C and G-C are both about 27.75 VAC. When thermostat is pulled off wall while in cool mode both Y-C and G-C drop to near 0.With cool on we have nothing at the contactor coil, plunger is not pulled down - 248 VAC into contactor. Fan starts when plunger is pushed manually.
Expert:  airheatman replied 8 months ago.

OK look in main drain line and see if perhaps there is a float switch or if you have an aux drain pan. look for a float switch on pan and lets see if we can find what is breaking the circuit to outdoor unit.

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