A/C question

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PTownSubbie

PTownSubbie

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Well, I made it to Illinois in time for my Mother's A/C unit to go on the fritz. It won't start. My brother and I did some poking around and we believe it is the capacitor (since that is a common failure).

Here were the symptoms. The fan would not start on the outside unit. When the signal to turn on the A/C was received, you can hear the compressor start and run for a short period; then turn off. We discovered that the compressor was turning off on High Pressure and had to be reset. So, when the compressor was running, I pushed the condensor's fan and it finally started spinning. This tells me the capacitor is bad..... Anyone agree?

Here is the big question though....will running that fan with the capacitor bad cause any damage. I tend to believe that it may not as the capacitor is really a start capacitor, isn't it? I don't want to cause any further damage but it is damn hot here! I would like to leave it running if we can...

Thanks for the quick help and I am headed to the A/C store first thing in the morning to get a new capacitor!!

So much fun.....
 
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you will need to push start it each time until you replace the motor (easier to replace the whole thing as most have the capacitor built in now). The motor will eventually fail completely.

I have one in my shop if you want to come pick it up. :wink: Replaced it a year before the air exchange fan went out in the attic. New system installed and I wasn't about to throw away a perfectly good fan motor.
 
You need to go to your AC supply plce and get a "hard start" capacitor. They should be around $35. Make sure to take your old one or write down every bit of info you can before you go down. That should fix your issue. If it doesn't I would start looking at the compressor.
 
Is this "hard start" capacitor the one that has three leads on the top of it or is it mounted on the fan motor?

Mike has me scratching my head....this might be a bad fan capacitor.....?
 
Fred:
A little more information, please. When you start the motor "by hand", is just the fan running? Or, is the unit producing "chilled air".

Checking for a functioning compressor can be done by putting a thermometer in front of a supply vent and measuring the temp. If the air coming from the vent is not at least 15 degrees cooler than "room" temp, the compressor may not be working.

Additionally, in weather this hot, there will be be condensation coming from the drain line, IF the compressor is working.

If these two things are happening, the odds are very good that is is one of two capacitors.

BEFORE OPENING THE OUTSIDE UNIT, disconnect the outside unit at the disconnect located very near the outside unit. ADDITIONALLY, USE ONE HAND and very careful disconnecting the leads from the bad capicitor (a shot capicitor can usually be "observed" by being dome topped, split or very black at the terminals). A bad capicitor can discharge great voltage and amperage more easily that a good cap.

Finally, IF the run/start cap is bad, make sure to clean/replace the indoor filters, clean the indoor evap coil if it can be easily reached, AND clean the cooling fins on the outdoor unit.

Popped caps are generally always caused by over work. In this hot weather, clean filters and coils are a MUST.

Respectfully submitted.
 
PenMan1 said:
Fred:
A little more information, please. When you start the motor "by hand", is just the fan running? Or, is the unit producing "chilled air".
System is running and cooling the house. The compressor seems to be operating just fine. It was tripping out on over pressure since the fan wouldn't run and cool the refrigerant. Since I push started the fan, it has been running and cooling but likely won't restart if it shuts off tonight....

Checking for a functioning compressor can be done by putting a thermometer in front of a supply vent and measuring the temp. If the air coming from the vent is not at least 15 degrees cooler than "room" temp, the compressor may not be working.

Additionally, in weather this hot, there will be be condensation coming from the drain line, IF the compressor is working.

If these two things are happening, the odds are very good that is is one of two capacitors.

BEFORE OPENING THE OUTSIDE UNIT, disconnect the outside unit at the disconnect located very near the outside unit. ADDITIONALLY, USE ONE HAND and very careful disconnecting the leads from the bad capicitor (a shot capicitor can usually be "observed" by being dome topped, split or very black at the terminals). A bad capicitor can discharge great voltage and amperage more easily that a good cap.

Finally, IF the run/start cap is bad, make sure to clean/replace the indoor filters, clean the indoor evap coil if it can be easily reached, AND clean the cooling fins on the outdoor unit.

Popped caps are generally always caused by over work. In this hot weather, clean filters and coils are a MUST.

Respectfully submitted.
Click to expand...

I originally thought it was the cylindrical capacitor but I don't think it is popped but this capacitor is for the compressor...is it not?
 
Fred:
It does sound like the start capacitor. Since you have to go to the HVAC supply house anyway, I'd get BOTH capacitors.

Depending in the mfg of the unit, the cap located near the bottom of the unit is usually for the compressor. The higher one is usually the fan or start capacitor. In this heat, the unit could easily be overworked. Changing one cap could easily "pop" the other when you put the unit back on line.

I'd spend $50 to replace both caps and make just one trip, but the nearest HVAC parts store here is 50 miles away.
 
navycop said:
I believe there are 2 capacitors. One on the outside unit for the contactor and another on the airhandler for the squirrel cage motor..
Click to expand...

Mike, You are right. The air handler is working fine though. Never had a problem with that. The problem is with the fan on the outside condensor unit.

PenMan1 said:
Fred:
It does sound like the start capacitor. Since you have to go to the HVAC supply house anyway, I'd get BOTH capacitors.

Depending in the mfg of the unit, the cap located near the bottom of the unit is usually for the compressor. The higher one is usually the fan or start capacitor. In this heat, the unit could easily be overworked. Changing one cap could easily "pop" the other when you put the unit back on line.

I'd spend $50 to replace both caps and make just one trip, but the nearest HVAC parts store here is 50 miles away.
Click to expand...


I think there is only 1 capacitor in the outside unit. The capacitor for the condensor fan motor is likely mounted on the fan itself..... I will have to check in the morning for that one.....
 
Fred,
I fix a/c in Florida. Most all fans and compressors you will see have a run capacitor. Only the compressed will have a start capacitor and start relay. The unit may have a duel run capacitor. Meaning that both the compressor and the out door fan use the same run capacitor.
The one for the fan will be a lower number like 5 or7.5 the compressor will be a 35 or 45 or on big units a 65. Capacitors are cheap. Under15.00. The expensive part is knowing how to wire them up. It is really easy for a single type capactor you must by the same size that is number on the low side, the 5 or 7.5 or 10. The other number will be 370 or 440. You can us a 440 in place of a 370. Really you can. But the smaller number must be exactly correct. It might have a very small plus on it. Pay attention as to whitch wire that is. Sometime but not always it matters. If it is a duel capacitor by the correct one and swap the wires. Take several pictures of it before you take it out. You will not remember how they go later. Trust me on this. One other thought if you have not had a tune up and drain line clean lately, you just my have a repair man come and do one for you. The cost for the cap from the repair man should be 125.00 or less a duel cap will be more because unfortunately you are having to replace 2 caps instead of one. The tune up could cost as much as 139.00. Good luck
It is easier said than done and they do bit if you touch them the wrong way.
If you run the unit with out changing the capacitor you will burn up the motor for sure.
Tom
 
Picked up a capacitor this morning and replaced it. The fan and compressor kicked over right away with no issues.

Thanks goodness it was that easy! The house is cooling again and just in time since they are predicting three digit temps today!!
 
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