AC unit (heat pump) clicks but no start.

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Old 05-01-14, 07:46 PM
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AC unit (heat pump) clicks but no start.

Hey all, first time posting here, great site!

Ok, my outside unit clicks once and nothing after that, the condenser fan doesn't come on and the compressor doesn't hum. I replaced the capacitor today but still same symptoms. I removed the fan motor (the fan is not seized) to have it tested tomorrow. My fluke is at work because I was so certain the cap went bad otherwise I would check power to fan motor.

The evap isn't freezing and there are no signs of freon leaking (the evaporator is about a year old).

If the fan motor tests good what should my next step be? Check voltage at the contactor?

Thanks for looking, any advice is welcomed.
 
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Old 05-01-14, 08:13 PM
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Welcome to the forums.

Yes... check contactor for burned contacts and 240vac.
 
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Old 05-01-14, 08:16 PM
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If you have click at contactor it's either a line voltage issue or possibly ants lizard wasp or mouse could be in contact not allowing voltage transfer. Kill power with screwdriver push contactor in visually inspect for debris in contacts. If clear then you need to check disconnect if you have 1. It will be a box mounted on wall with electrical whip line coming from it to unit. Open it check voltage inside it. There may be fuses in this disconnect. Ohm them if ohm setting buzzes fuses are good. You need to pull both from holder to check. If power is present fuses ohm out check breaker at breaker box. It should be double pole single throw prob 50 amp. If breaker in on position you may need to pull breaker cover to access wiring leaving panel test voltage out of breaker. It is a power issue. You just have to find outage point. Good luck. Hit me back if all fails.
 
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Old 05-01-14, 09:14 PM
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Thanks for the replies, I'll bring meter home and start checking it out after work and will definitely report back.
 
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Old 05-02-14, 04:35 PM
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Update: I took a look at the contactor and found wasp debris on one pole and the other pole that the compressor and cap go to (small red wire and a bigger red one) had burned spots on the contact. The poles had continuity when depressed though and the coil ohmed at 8.1 ohms. I replaced the contactor anyway because it looked pretty rough, still only getting the single click.

I pressed the new contactor in manually and everything came on as it should, sounded fine, so definitely a control voltage issue, the contactor never closes.

I have 120ish on each leg and 248 volts total at the safety disconnect box on the side of the house. I do not have 28 volts at low voltage side of contactor (coil), I jumped the red and yellow wires at the T-stat but no dice, I think I have a bad circuit board in the outside unit.

Thanks for any guidance, it is appreciated.
 

Last edited by Chopper Guy; 05-02-14 at 06:31 PM.
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Old 05-02-14, 07:40 PM
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Ok...... you should have two wires going from the air handler to the compressor unit. Usually they enter an access panel near the electric and they are wire nutted together. Remove the wire nuts and check there for 24vac. If it's there - then the problem is in the compressor unit.

Is this a straight A/C unit or a heatpump system ?
 
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Old 05-03-14, 05:01 AM
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Hmm, heat pump system I believe. My air handler is in the garage and my outside unit is on the opposite end of the house. I'm not entirely sure where to look for the two wires you are describing even though you mentioned an access panel near the electric. There are several sets of small wires wire nutted in the access panel on the outside unit near the contactor etc though. Maybe there?
 
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Old 05-03-14, 05:51 AM
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There should be a small gauge wire set (wrapped in a jacket) coming from the house and going into the compressor unit. This is the low voltage (24VAC) control signal coming from the thermostat. When the voltage between these two wires is 24V, the thermostat is calling for cooling and this energizes the contactor, turning on the compressor unit. This is the wire that PJmax wants you to disconnect and check for voltage (on the wires coming from the house). Make sure that the thermostat is calling for cooling (or you have the R & Y wires jumpered).
 
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Old 05-03-14, 07:27 AM
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Ok, I have 26v at R and Y behind the wire nuts when calling and 28 when not. I jumped them and the contactor closed and the unit started running. I undid the wires and only checked the very small R and Y wires from house and only have 12 vac.

I measured voltage at the thermostat in the house between R and Y and have 28vac off and 0 on.
 

Last edited by Chopper Guy; 05-03-14 at 08:46 AM.
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Old 05-03-14, 09:21 AM
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I'm afraid you've lost me. The 24VAC should be coming from the wires running from the house (via the thermostat). I understand you to say that when you disconnected the wires coming from the house, where they attach inside the outside unit, you only have 12VAC, yet you have 26/28VAC with the wires attached to the internal wiring inside the compressor unit? Also, you said that you jumped some wires and the contactor closed and the unit started running. What exactly did you jumper?
 
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Old 05-03-14, 09:50 AM
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Sorry. I checked the red and yellow wires that are wire tied together, small yellow and bigger yellow and small red and bigger red and got 26 or 28v. I separated them and only checked the small wires (Thermostat) and have 12vac. This may not be a valid check, I don't know, but inside at the stat I showed 28vac off and 0vac on but only 12 outside on just those small wires.

I jumped the small/big red to the small/big yellow that normally have wire nuts on them and the contactor closed and the unit ran fine.

I'm currently in the process of jumping the low pressure switch.

Update: the unit did not come on when jumping the Low pressure switch.
 

Last edited by Chopper Guy; 05-03-14 at 10:22 AM.
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Old 05-03-14, 10:44 AM
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You'll have to wait for Houston or PJmax to respond. I'm just a knowledgeable homeowner, but what you're saying (if I'm understanding you correctly) doesn't make sense. To my knowledge, the 24VAC that goes to the contactor (to close it and run the compressor) comes from a 24VAC transformer inside the house (usually in the air handler). The 24VAC passes through the thermostat and is sent outdoors to the condensor unit (small yellow/red wires in your case). There shouldn't be another source of 24VAC in the condensor unit, so I don't understand how the voltage across the Yellow/Red wires INCREASES when they are connected to the condensor Yellow/Red (heavier wires) wires versus when the wires (from the house) are disconnected from the condensor wires. Also, if you jumper across the Yellow and Red wires (that go to the contactor), you should be shorting out the 24VAC coming from the transformer and should prevent the contactor from closing, yet you say that it closes the contactor. I must be missing something major here.
 
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Old 05-03-14, 11:14 AM
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Chopper..
When we discuss colors we are only using the colors of the wire in the multi wire cable. From your air handler to your compressor is a multiwire cable.

How many wires are connected from that cable to your compressor unit ?

A heat pump system is where the outside compressor runs in the winter to supply heat.
Does yours do that ?

Since you got the contactor to respond you must be sending power outside.
 
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Old 05-03-14, 11:58 AM
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Okay, i have 3 wires from the multi wire cable, red, yellow and blue. I have a heat pump system. I agree that when I jump the red and yellow wires on my unit and the contactor closes and the system blows cold that the correct voltage must be present.

I don't understand the relationship between the defroster board and the contactor, I'd like to verify voltage in voltage out in order to eliminate the board as a culprit.
 
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Old 05-03-14, 12:07 PM
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Ok... so you have a heat pump.

You have three wires in use. (usually more on a heat pump)
One is compressor
One is common
One is reversing valve (for selecting heating or cooling mode)

When you mention "jump the red and yellow" you are talking about inside at the air handler... correct ?

The defrost board is there to defrost the outside coils in the winter. It's job is to shut down the compressor, activate the reversing valve, turn on electric heat (if available).
A make and model of your compressor unit would be helpful too.
 
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Old 05-03-14, 01:23 PM
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No, when I jump the red and yellow wires it's out at the compressor unit, I remove the wire nuts and jump it right there. I jumped it at the T-stat last night but it just clicked outside.

I'll get the compressor info and post it soon.
 
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Old 05-03-14, 01:32 PM
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It sounds like possibly a missing/broken wire.

Red = 24vac
Yellow = compressor
Blue = common or reversing valve
?? = common or reversing valve
 
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Old 05-04-14, 08:03 PM
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Your right, I didn't see the other two wires, they are brown and white. So I have red, yellow, blue, brown and white. It being a control issue I (I'm sure I'll get scorned for this) jumped the red and yellow wires at the outside unit and let it run for several hours to cool the house down, I've done this 3 or 4 times now, it runs and cools perfectly. When it was on this long I noticed the condensation pump at the air handler was not coming on. It seems it isn't being told that the compressor unit is on? Is there a feedback/reference for this from the outside unit to the air handler/condensation pump?

My outside unit has been in service since 1997 FYI.
 

Last edited by Chopper Guy; 05-04-14 at 08:20 PM.
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Old 05-05-14, 05:01 AM
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I have a condensate pump on my system as well. There is a reservoir with a float at the bottom of the pump. When the water level rises to a preset level, the float rises and turns on the pump which pumps the condensate out. The pump won't run again until enough water has built up that the float rises enough to turn the pump on again. In other words, it's not supposed to run continuously.
 
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Old 05-05-14, 07:08 AM
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Yeah, it wasn't coming on at all, water was getting all over the garage floor. This main problem, control voltage not present at contactor, has gone on long enough for me, I've learned a lot, I know what it's not, but it's time to call an HVAC pro, it's supposed to be close to 90F today.

I will post what the problem ends up being, I hate following threads and the fix is never posted.

Thanks for the advice thus far!
 
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Old 05-05-14, 09:15 PM
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Sigh......it was the silly float switch in the condensation pump. The HVAC tech jumped it and all was good.
 
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