AC will not start


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Old 05-18-08, 09:43 PM
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AC will not start

I recognize this is a common topic. I was not able to find any answers from other posts on this issue.

I have a Lennox xc15 professionally installed just under 2 years ago. Worked great the first two seasons. Went to start it up this weekend and no joy. Thermostat and blower fan on the furnace seem to be functional. New air filter is in place. Neither the fan or the compressor will start.

Cursory inspection of the house breaker panel did not reveal a problem.

I removed the service panel on the AC unit to read the system operation monitor. It has a 3 LED system. I have a green Power LED on, yellow alert LED off, and a red trip LED on. The unit's manual describes this scenario as follows:

24VAC power is present at the module terminal.
System and compressor check out OK.
Thermostat demand signal Y1 is present, but compressor not running.

The manual also gives trouble shooting instructions/possible problem sources which I am not sure I understand:

1 Verify Y terminal is connected to 24VAC at contactor coil. I think it is but not sure
2 Verify voltage at contactor coil falls below 0.5VAC when off. I don't have an ohm's meter or the equipment to check this
3. Verify 24VAC is present across Y and C when thermostat demand signal is present; if not present R and C wires are reversed. Huh?
4. Compressor protector is open. I don't think it is
5. Outdoor unit power disconnect is open I'm sure it is not
6. Compressor circuit breaker or fuse is open I don't see where this is located
7. Broken wire or connector is not making contact Can't see any evidence of this but not sure
8. Low pressure switch open is present in the system. Have no idea here
9. Compressor contactor has failed to close. Again, no idea

While inspecting the outdoor unit I did clean out the coil with a hose because it was pretty dirty. This was after it had been malfunctioning, not before. Also, there are some leaves at the bottom of the unit I can't get too.

Sorry about the long post. I thought the specific info might help others.

Any ideas would be appreciated. I've already planning on contacting the HVAC company tomorrow. I would just like to hear some objective trouble shooting advice/know how.

Thank you.
 
  #2  
Old 05-19-08, 02:21 PM
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Originally Posted by humid
1 Verify Y terminal is connected to 24VAC at contactor coil. I think it is but not sure
Do you see a button on the coil that you can press down on to see if you are getting power to it?

2 Verify voltage at contactor coil falls below 0.5VAC when off. I don't have an ohm's meter or the equipment to check this
Will be needing this if you find out that there is power to the unit from my suggestion above.


3. Verify 24VAC is present across Y and C when thermostat demand signal is present; if not present R and C wires are reversed. Huh?
I wouldn't worry about this, if the unit has been working, then it's fine.

4. Compressor protector is open. I don't think it is
What makes you say that?

5. Outdoor unit power disconnect is open I'm sure it is not
Checked to make sure it's turned on?

6. Compressor circuit breaker or fuse is open I don't see where this is located
Breaker should be in your main panel that service the house, and or may have one in your disconnect box next to the unit.

8. Low pressure switch open is present in the system. Have no idea here
We won't know till you get a meter to check things out.
 
 

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