AC no longer cooling, anything I can check?

Reply

  #1  
Old 09-30-18, 06:28 AM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
AC no longer cooling, anything I can check?

Yesterday afternoon I got home to find the house at 80F, the thermostat set at 74F. After checking to make sure the power had not gone out during the day, I felt the air blowing through the vents to find it not blowing cold at all.

Checked the outside unit and it was running fine, no unusual noises. Checked the filter on the inside unit, I had changed it fairly recently so it's dirty but not too bad (going to replace it today, just to be certain). The indoor unit is also not making any unusual noises. No visible frost or icing on the lines leading to the outdoor unit or coming out of the inside unit.

A couple years back a tech told me the refrigerant was low and that I should replace the whole system. However, it was blowing plenty cold (checked with a thermometer myself) and they definitely appeared as though they were simply trying to sell me a new system. It's been fine until yesterday. Indoor unit is a Trane 2TGB, Trane XR13 outdoor unit and approximately 10 years old, maybe closer to 11.

Before I call a service tech out tomorrow, is there anything else I can check?

Thanks.
 
Sponsored Links
  #2  
Old 09-30-18, 06:41 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,400
You said that the outside unit (compressor/condenser) is running. Can you tell if the compressor is running, or is it just the condenser fan (fan on top of unit)? If you're not sure, check the two copper lines coming out of the outside unit. The larger diameter one (usually has some insulation on it) should be cold, while the smaller diameter line should be warm to hot. Since it's not cooling, I'm guessing you'll find that both lines are approximately ambient temperature.

Many systems have a low pressure cutoff switch. This is in series with the 24VAC control voltage in the outside unit. It prevents the compressor from turning on if the system is too low on refrigerant to prevent damage to the compressor. However, if your system has a low pressure switch and it "kicked in", your condenser fan wouldn't be running either, which you indicated is not the case.

One thing you could try is to replace the capacitor(s) in the outside unit. There are usually 2 capacitors used, one for the compressor and the other for the condenser fan. They are often in the same "can" (what's referred to as a dual capacitor), however some systems use two separate capacitors.

Turn off the power to the outside unit (there should be an electrical disconnect box nearby), remove the access panel and take a look inside. If the top of the capacitor looks bulged, that's a pretty good sign that it's bad. However, even if it looks good, capacitors are pretty inexpensive, often <$20. Just be sure to match the capacitance (expressed in mfd) and that the voltage rating is the same or higher than the original. When you replace it, pay attention to the markings on the capacitor. Usually (for a dual cap) you will see the following markings for the terminals: C (common), H or Herm (compressor), and F (fan). Make sure that you wire the new one the same as the old one. I would suggest that you take a picture or two of the old capacitor & wiring before removing it.

Good Luck!!
 
  #3  
Old 09-30-18, 07:05 AM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
Thanks, I will switch it on shortly and check the lines. I have had the cover on the outside removed previously, I believe mine has 2 capacitors (was originally one, but at some point it was replaced with 2).

A picture of the wiring is a great tip, anytime I take something apart I typically will do that. Assuming the capacitors look like they need to be replaced, should I leave the petpo off for a short time before removing them to let them discharge? Additionally, can capacitors be purchased at places like Lowe's? I remember calling an HVAC supplier a while back to ask about a replacement fan motor and they would not sell it to me unless I had an HVAC license.

Edit: after about 5 minutes of running, both pipes still the same temperature. The compressor was replaced a couple years (at most 4) ago, hopefully that's not broken again.
 

Last edited by naiku; 09-30-18 at 07:33 AM.
  #4  
Old 09-30-18, 07:41 AM
Join Date: Sep 2018
Location: usa
Posts: 16
as an aside for those who don't know, if you do start fooling with the capacitors, take care not to touch the terminals, loaded capacitors bite. Their function is to store energy and release it quickly, used to give a shove (so to speak) when starting a motor for instance where there may be lots of resistance (as in a compressor)
 
  #5  
Old 09-30-18, 08:02 AM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
Great advice about the capacitor, I am always careful around them.
​​​​​​
I took the cover off to look at the caps, this is what I see:





The kickstart looks toast, the top has seperated. Am I right in that the purpose of that is to start the compressor? Should I also replace those others while I am in there?
 
  #6  
Old 09-30-18, 02:32 PM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,400
I agree with you, it looks like the kickstart capacitor has "blown it's top". Usually, a kickstart circuit has a capacitor and a relay. Make sure that the kickstart cap is just a capacitor and that there's not anything more inside.

In the picture with the two capacitors, the 5.5mfd oval cap is for the fan, the round cap is for the compressor. It's hard to tell from the picture whether the top is bulged or not.

I know that Amazon has capacitors. Some industrial supply houses (Graingers, etc.) often stock them too.
 
  #7  
Old 09-30-18, 02:42 PM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
When searching for the kickstart, it looks like it includes a small black box as well, I did not see that in mine, but also did not look so it's possible it's there. See here:

https://www.amazon.com/Rectorseal-96503-Kickstart-T05/dp/B008A3UJ82?keywords=021449965033&qid=1538321070&sr=8-1&ref=mp_s_a_1_1


The round capacitor looked ok to me, I might replace it though. Is there a difference, other than price, in these 2? The first is exactly the same as the one in there, the second matches specs but it's a quarter of the price.

https://www.amazon.com/27L20-Upgraded-Replacement-Round-Capacitor/dp/B06XRMRZ35

https://www.amazon.com/Trane-CPT00659-CPT-0659-Replacement-Capacitor/dp/B00RZXUT0G?crid=1AJ4MO0IOO2OV&keywords=cpt00659+capacitor&qid=1538343705&sprefix=cpt00659&sr=8-1&ref=mp_s_a_1_1
 
  #8  
Old 09-30-18, 03:55 PM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,400
Almost all capacitors you buy today are made in China. Personally, I would go with the cheaper Genteq. I doubt that the GE is any higher quality.

I suspect the "black box" on the kickstart is the relay I mentioned earlier. Assuming you have the black box, you should be able to just replace the kickstart capacitor. I didn't know if the relay was contained within the kickstart capacitor housing (unlikely but possible).

The "blown" kickstart capacitor is likely the cause of the compressor not starting, but for an additional $10, it might be worth it to replace the compressor capacitor as well.
 
  #9  
Old 09-30-18, 04:11 PM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
Thanks, that's what I was thinking as well, $10 and I am already in there with the power off etc. Going to call a local supplier tomorrow to see if they stock them, if not will order from Amazon.

Fingers crossed in a couple days it's working nicely again. In a house with 3 boys and no working AC it's been miserable!
 
  #10  
Old 10-01-18, 03:59 PM
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 146
Found a local supplier, $35 for the kick start and $7 for the capacitor. I ended up just replacing the kick start for now, figured I would keep the other on the shelf as a spare in case the other cap does fail.

Working nicely now, taking a while to get the house cooled down, but it was reading 81F when I powered it back on.
 
  #11  
Old 10-02-18, 04:38 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,400
Congrats on the repair! Glad to hear you got it up & running again.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes