replaced contactor/cap, still only starts manually


  #1  
Old 12-31-18, 01:18 PM
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replaced contactor/cap, still only starts manually

Update: no power at outside unit. 5 amp fuse blown at air handler, could it be the transformer?
3-4 years ago the contactor failed so I replaced the contactor and cap (while I was in there) and everything was good as new.

2 days ago I realized the condensor fan and compressor weren't engaging. I put my old cap (tested:good, kept as spare) back in, no start. Manually engaged contactor, everything kicked on. Brought a new cap and contactor home and installed today (keeping old good cap as spare :-) ).
I was feeling pretty proud of myself until I powered all the breakers back up and still nothing. I can manually engage the new contactor and the fan/compressor come on. Once I let go, everything stops.
I tried directly wiring, bypassing the tstat and applying direct voltage to green and yellow wire (to eliminate tsat failure). The blower comes on, but still no condensor fan/compressor.
I haven't checked system charge yet, but my assumption (fwiw) is the system would have to run long enough for a low pressure switch to activate if there was a low charge, I get nothing.

I assume my next step is to check voltage at the yellow tstat wire that engages the coil on the contactor. Any ideas?
I'm handy with home wiring and restoration, I work in the automotive air conditioning field so the concepts are familiar, but this is really annoying. I'd love to trace for continuity from air handler board to outside wiring, but my Fluke leads aren't long enough LOL. There is probably something simple I just don't know to look for.

Any/all help appreciated.

 

Last edited by Ducss; 12-31-18 at 02:30 PM. Reason: Update
  #2  
Old 12-31-18, 04:21 PM
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Welcome to the forums.

Check for 24vAC where the thermostat wiring connects to the condenser first..... not at the contactor. There should be wirenuts at the connection point and it may be inside the wiring junction area. If you have the voltage at this point but not at the contactor...... more than likely you are low on refrigerant charge.

As the outside temps go down...... there is lower starting pressure in the system. This would be the time you'd be affected by low refrigerant.
 
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Old 01-02-19, 11:17 AM
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Thanks PJMax

I checked at the outside unit. The yellow wire shows no voltage using either condensor chassis ground or condensor motor ground.
I ran a sniffer around, no leakage detected. Temp isn't an issue, it's a balmy 78 in Florida right now :-)
I'll measure output at the transformer this evening and update.

Thanks again!
 
  #4  
Old 01-02-19, 11:19 AM
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Don’t measure to ground. Measure across the circuit.
 
  #5  
Old 01-02-19, 04:41 PM
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Look into an overflow condensate switch issue too. If it's tripped it will remove power from the Y line.
 
 

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