My home air conditioning / heat only blows ambient temperature air through the vents, there is no temperature change through the unit. Inspecting it, the condensor fan is spinning, as is the evaporator fan (since I feel the air from the vents). I'm hearing a strange noise from what I assume is the compressor, and the lights in my house dim when the noise is occurring.

Here is a video of it happening: https://photos.app.goo.gl/ZQc6V8ojNN4qEFAW2 . The lights dim when the "hum" occurs.

I don't have the tools to check the refrigerant pressures, but I am comfortable with electrical. Is it worth trying to inspect the capacitor, or do I likely have other issues?

I have a Goodman Packaged Unit/RTU Model PHKJ042-1. No breakers are tripped, cycling them has no effect.

  • 1
    Turn it off, now. You could try a new cap; that's like a $10 try. Compressor's prob shot, which means buying a whole new condenser. I've never know anyone to replace a compressor inside of a condenser. Verify you've got 220 at the condenser.
    – Mazura
    Mar 11, 2018 at 0:21
  • I forgot to mention, the household lights dim when the humming occurs.
    – Jeff
    Mar 11, 2018 at 0:46
  • 1
    Try the cap first, but that is usually for the condensor fan and not the compressor. Now, weight the costs of repair vs replace. Don't just jump to replace if the compressor is fairly new, uses a lower cost refrigerant and can be swapped easily. An HVAC tech will need to do this because of the refrigerant. The compressor will make some noise as it is compressing the refrigerant, however, dimming the lights means an excessive draw of power.
    – Jeff Cates
    Mar 11, 2018 at 4:48
  • It could also be fine, and you may have a leak in the refrigerant lines, therefore the compressor is not working properly. Best to get it checked by a tech and go from there. I had someone tell me I needed to replace my condensing unit because it groaned and didn't cool the home. Turned out to be a leak discovered by myself while it was running. I heard a hissing and the filter had a leak in one end. I replaced the filter, called a different company out. He vacuumed the system, held vac and so he charged it up. A year later it still works like new. The first company looked at how old the unit
    – Jeff Cates
    Mar 11, 2018 at 4:53
  • 1
    My unit has a sensor called "Loss of Charge Protection" which I will assume is a low pressure switch. Given the compressor buzzing, I'm guessing I have refrigerant
    – Jeff
    Mar 12, 2018 at 0:11

1 Answer 1


I am suspecting that you do not have the correct power and possibly a capacitor is out as well.

I am going to state a couple observation about your video so read closely.

I am looking at your video post and watching the SLOW moving Condenser Fan and I also heard the BUZZ.

As for the condenser fan it seems like your RUN circuit is not powered up - this can be one of a couple things depending on how that motor is wired - and if it is 220V. Run Capacitor could be bad. However I suspect that you have a BAD phase feeding the AC unit. The reason being is that your compressor is not running either.

Please Check your power coming off of your Circuit Breakers - check it at the Terminals of the Condenser Unit . You should have L1 and L2, check L1 - N(115V), L2 -N(115V), L1-G (115V), L2-G (115V) , L1- L2 (230V). I am suspecting a Circuit Breaker has high resistance and either not supplying power or supplying very little power - when measuring at the condenser watch which line (L1 or L2) DROPS when you start the unit up. That will tell you which side of the breaker is bad or possibly your contactor, You will need to measure on both sides of your contactor while doing this check (contactor only pulls in when compressor is told to run) Contactor T1 and Neutral , T2 and Neutral - you will need to verify both sides to know whether you have a bad contactor or a bad circuit breaker.

If you can post a picture of the wiring diagram found inside the panel cover that will help tremendously. Then I will know how that motor is configured for start winding or not.

When checking your capacitor (always be careful to discharge them before handling as you can get electrocuted [aka Killed] or shocked. To discharge them using a screw driver between Common and Herm or Fan (only handling the insulated part of the screw driver).

If your meter does not check Farads you can test the capacitor in the unit while the unit is "running" - well in your case on.

Measure the current (amps) of the motor start winding coming off of the capacitor (herm lead and also for the Fan lead) and multiply it times 2652 [in USA 60Hz numbers] then divide that number by the voltage you measure across the capacitor. This will tell the Farads of the capacitor and it should match the capacitor or be with in say 5% , sometimes 10% could be ok depending on the quality of the capacitor.

With the measurements you made; if you were to assume your capacitor was working you would find what current you should expect across those winding's Herm (yellow according to your diagram) and Fan (Brown according to your diagram).

From your Measurements on the Fan, I used a pseudo value of 1 amp on the winding using that number your Fan capacitor is at 106 UF but the 5 UF capacitor is a typical proper sizing for a Fan motor. (1 AMP * 2652 ) / 25VAC = 106 UF you can see the amperage I have used is about 21 times too high so 1/21 = .0476 - I am sure that is too low of a current draw to start that motor - so I suspect Capacitor is bad.

Using the same Formula on the HERM (Compressor Side) your measurement was 240V So just assuming a low Amperage of 1 AMP (1 AMP * 2652 ) / 240VAC = 11.5 UF your capacitor is supposed to be 50UF or about 4.7 times greater than what our pseudo value gives us. So if you measured with an Amp Meter that the compressor was drawing roughly 4.5 ~ 5.0 Amps on that winding (yellow wire going from Capacitor to compressor) the capacitor for that side would be working.

Given the capacitor is bulging I suspect at least the capacitor has failed especially given your measurements - I know the fan side can't be working if that was truly the fan side you measured.

Now a suspicion I have about the readings you gave me .. If perhaps you mixed them up and got them backwards.. ~25V was on the HERM side and 240V was on the fan side the fan side would be working and the compressor side would not be working. Bad Capacitor.

50UF should be your compressor side and 5UF should be the AC Fan side. Your part number if my search was correct should be this: PPS550440RD ; However a capacitor that is a Dual 50UF & 5UF rated for 440 VAC will work fine. While your capacitor in the image is 370V , the higher voltage 440VAC has a little more headroom and your situation requires it .. 370V is typical in a 220V circuit here is the formula 1.56 * 220V = 343 VAC, However you have measured 240V which 1.56 * 240 V = 374 VAC and that is OVER the rating of your capacitor and therefore it probably went BULGE no worky after a while. So get one rated at 440CVAC or even 470 VAC.

  • The diagram is very weathered, but here's the same model from the S/M photos.app.goo.gl/kewfwRYXByOu2h9I3 . I didn't realize the condensor fan was slow, and I will check the contactors tomorrow. Thank you
    – Jeff
    Mar 12, 2018 at 0:00
  • I will also mention my unit does not have the start assist component (resistor?) next to the dual cap (Cap.1)
    – Jeff
    Mar 12, 2018 at 0:06
  • @Jeff I would check L2 & Neutral on the incoming side of the contactor ,AC Thermostat AC is OFF but Circuit Breaker's ON. Then I would check T2 opposite side of Contactor AC On and Calling for Cooling. According to the diagram it looks like there is a Red Wire that goes from T2 to Center Tap of Capacitor and also to the Compressor, I suspect low or no voltage at T2. The cap could be bad but check this first as it is in common with both and not usual that the cap blew both sides (it could but not usual). You can also unplug center tap check voltage on T2 if good now capacitor probly shorted.
    – Ken
    Mar 12, 2018 at 2:54
  • Confirmed the contactor is fine, I didn't realize they'd have an open air casing. But verified it closes and passes 240v on both sides. With compressor activated, there is 240v on the common side of the cap, 240v on the "herm" compressor side, and only ~25v on the fan side. I hsould note when doing this test the condensor fan no longer spun as well. I've also measured 240v at the condensor fan when commanded on between common and the purple wire.
    – Jeff
    Mar 12, 2018 at 23:56
  • 2
    I was testing the contactor while commanding cooling on, I did not push on it. The voltage readings were correct, as the fan had stopped working as I stated. But the capacitor fixed it! Thank you for your help, I learned a lot about this system. I finally see where my auxiliary heating is (it wasn't working last winter), and I was able to wire in a common wire for the thermostat. The Nest thermostat was current sapping to charge but now has a common feed. You guys have been amazingly helpful, thank you!
    – Jeff
    Mar 13, 2018 at 23:41

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