Hi, last year about this same time the AC stopped blowing cool upstairs and I notice outside unit not starting up. Long story short I ended up called a tech and he replaced the run capacitor in the outside (upstairs) unit. I paid quite a pretty penny for this quick job.

Fast forward to this week and same same exact symptoms on the downstairs unit. So I buy a spec matching new one from Amazon and replace it following some best practices on youtube.

Unfortunately, no improvement. I do a basic multi-meter test on the old one and the readings jump around when set at 200M ohms so I'm guessing its still good?

What else can I troubleshoot here? I've attached pics of old and new caps in case you see something off there. And does it matter which posts are used to connect the wires for each connection? Also, I see that the old one only had 1 post for the FAN connection. Thanks in advance.

 

Are you sure it's the SAME exact symptoms ?
There could be one of many problems.
Replacing the cap was a good idea but not the problem.
When you put the thermostat to cool does the contactor in the condenser pull in ?
Does the fan run ?
Does the compressor run ?
Do neither run ?
Does anything at all happen ?
If nothing happens you are more than likely low on refrigerant charge and the low pressure switch is keeping the unit from starting.

 

From what I can tell, nothing happens...no noise, no movement.

 

Is the contactor even pulling in?
Capacitors can be easily tested with the proper meter.
Test if the unit is calling to run.

 

I tested the old cap after replacing it (its 13 years old) but it seems good.

How do I check the contactor? Not familiar with that part.

 

By checking the coil for voltage. But you should be able to physically see if the contactor is open or closed.
capacitors are tested by measuring capacitance, not resistance.

 

Little confused on how to use my little meter then. I don't see a way to measure farads on it but if I set it to ohms (resistance?), I get a reading on the cap. Won't that tell me if functional? Also, see attached for pic of contactor. Plunger is out. Still not sure how I can check for "pull".

 

By "check coil for voltage" does that mean remove blue and yellow wires from previous pic, set meter to V (- or ~ ?) and make contact with the 2 leads?

 

General resistance check will not tell you if the capacitor is functional or not. You’d need a meter that reads capacitance.
But it’s not the issue anyway. The contactor isn’t closed. That unit isn’t calling to run.
Is there power to the contactor coil? Is the thermostat calling to run?
Don’t remove any wires. Troubleshooting will be done with live voltage, both high voltage and control voltage.
​​​​​​​

 

Bear with me, I'm pretty much a noob here. Are you saying that plunger should be depressed when off? Are you saying to turn breaker power back on and then do..what?

And its interesting that I found multiple videos saying to set the meter to ohms and then test the capacitor for readings.

 

The contactor will pull in when it closes, when the coil gets power.
That one is open and not attempting to start the unit.
So you’ll need to check and see if the coil is getting control voltage. If not you’ll have to start working upstream to see why the unit isn’t calling to run.
This will be all with power on and the thermostat set to call for cooling.

 

OK, is that something you can walk me through doing or am I in over my head? How would I check for voltage? I will restore power and turn on the AC...

 

These photos and information were taken with the unit off?
It needs to be on and calling to run. We need to determine if the unit is getting a call to run, and where the problem is.
If your not comfortable working with live high voltage then by all means call to get the issue diagnosed. Otherwise you can start troubleshooting with your meter.

 

Yes, all photos so far are with power off. Nothing seemed to change after restoring power and calling for AC.

I'm willing to try some things if we're talking common sense safety stuff...

 

First step will be turning power on and turning the thermostat to call for air conditioning. Does the contactor close? Does the condenser get a call to run?

 

No, there is no change in the contactor position nor does any part in the entire outside unit make any sound or movement.

 

Ok, is it getting a call to run?

 

I don't know what you mean by "call to run"?

 

Turn the power off the condenser.
Using your meter check for 24vAC at the blue and yellow wires on the contactor.

If no 24vAC is found there...... locate the thermostat cable to the condenser. It's typically small, roundish and brown. It connects near where the main AC power connects to the condenser. It will be spliced with wirenuts. Check for 24vAC at the wirenutted splices.

 

The thermostat will energize Y1. That’s where your looking for control voltage.

 

OK, I thought we were working with power on at this point...so breaker off and I get no reading from either V~ setting on my multi-meter.

 

If the air handler still has power, the thermostat is calling to run and no 24V is at the outdoor unit your issue is with the thermostat wire or in the air handler.

 

Sorry guys but I'm confused now whether the breaker to the condenser should be on or off so its still off.

Regarding, the thermostat wire, there are actually 3 wires coming in and each wire-nutted to another wire. I wasn't sure which 2 to check so checked every combination and got no readings.

The air handler in the attic seems to be function fine as it is blowing air out of the inside vents. So how could the air handler be part of the issue?

 

Power off. The voltage you are looking for comes from inside.

You do not have the connections to be tested in that picture. Those connections are the main AC. You need to look for a small two wire cable in the same area.

One wire will probably connect to the blue or yellow in the upper left corner of the picture.

Don't forget...... it may take your thermostat up to 5 minutes to send power outside to the condenser to protect the compressor from short cycling.

 

OK, assume you mean the wire in the pic below? The larger round wire seems to disappear in to the cage of the condenser and the blue and yellow are the ones connecting to each side of the contactor.

 

Yes..... that is the thermostat cable. You have more than two conductors but only two are connected.

Yes.... ultimately they connect to the blue and yellow contactor wires but we are looking for devices in one of the lines. So one incoming wire may connect to the yellow or blue. The other may pass thru a sensor and then to the blue or yellow wire.

Look for the wirenutted splices to check at.

 

You mean there should be more wires wire-nutted together than those 3? I don't recall seeing such but will check in the morning. Thanks for the help thus far.

 

Should only be 2 conductors for the thermostat bundle.
The 3 wire nuts you pictured earlier are line voltage.

 

We can see the wires go thru the metal frame. The splice is on the other side.

 

I pressed in the plunger and the fan and compressor started running. So something is preventing the plunger from depressing during normal operation, right?

 

Yes, you have no control voltage to pull the contactor in.
Please do not manually push in the contactor. It can be very dangerous or even deadly. Look up arc flash.

 

I did it with an insulated screwdriver but point taken, thanks. So how do I troubleshoot the control voltage?

 

You need 24V to the thermostat conductors to pull in the contactor.
So if no voltage is present at the wire nut connections at the condenser you need to start working your way upstream to see where the voltage is dropping out.
This needs to be done while the air handler is powered and thermostat calling for cooling.

 

OK, does the power need to be on at the condenser breaker outside as well during this testing?

 

Hi, with your meter set to AC Volts and the thermostat calling for cooling put your meter leads one each on the the blue and yellow terminals on the contactor, wait at least 5 minutes, you can also remove the thermostat and connect Y1 and R together to see if the contactor will pull in.
Main power to condenser can be turned OFF for this test and for your safety.
Geo

 

It does not need to be on, no.

 

OK, I finally got access to the wire-nuts you guys mentioned earlier. So I'm checking for AC voltage here by connecting a meter lead inside each nut, correct?

Then additionally farther downstream check for 24v again where the blue and yellow wires connect directly to the contactor?

 

No, if you don’t have 24V at the wire nuts then your headed towards the air handler for further testing.
The voltage source is the transformer in the air handler.

 

I checked for voltage at both places and got no reading...but there was very little room inside the wire nuts so I'm not sure I was making the correct contact. Can you clarify what I need to be touching in the wirenuts as well as at the contactor connections? Also, is my meter set correctly below?

 

You need to be touching the conductor in the wire nut.