Inside Unit Is Not Turning On

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  #1  
Old 07-23-20, 06:13 AM
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Inside Unit Is Not Turning On

When I turn on AC Interior unit is not coming on but the outside unit is running. I can hear the inside unit making a small constant humming noise but that's all.

In the past I have replaced capacitors, etc on the outside unit with everyone's help but I have never T/S the inside unit. T batteries are new.

Where do I start to T/Shoot this unit?

Edit
AC system is gas type
 
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  #2  
Old 07-23-20, 07:54 AM
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The make & model of your furnace/air handler would help. Do you know if you have a variable speed blower (inside)? There are two types of blower motors commonly used: PSC and ECM. PSC motors usually have a capacitor which could be bad. ECM motors don't use a capacitor and (unfortunately) are very expensive to replace.
 
  #3  
Old 07-23-20, 10:06 AM
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Check to see if blower wheel rotates freely and is not obstructed.

Next would do close visual inspection of inside unit printed circuit board. Often source of problem can be seen.

Before disconnecting board, take pictures to facilitate reconnecting wires

When removing board, be careful, many of the small wire connectors have tiny lock tabs that have to be pressed to unplug.

I had similar problem. See: https://www.doityourself.com/forum/a...ml#post2853722
 

Last edited by doughess; 07-23-20 at 10:40 AM.
  #4  
Old 07-23-20, 01:05 PM
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I will check model etc tonight when I get home from work
 
  #5  
Old 07-24-20, 07:26 AM
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Fixed!

Found the culprit. It was a wire nut connection. It was tight as it would be expected but it was full of greenish gooey liquid. Over time the leak droped onto the bottom of the cover. Only this one wire nut had this stuff. Removed the other wire nut and it was normal dry. The same stuff is at the prongs of the power cable. What is this stuff?






​Blower rotates very very freely but it was covered in too must dust. It has a capacitor. Does that confirm it is a PSC type motor and can you tell if it's a variable speed type?



Could not find the location of the printed circuit board. I still would like to get to it and dust if off.
The unit is a carrier, gas powered model 349FAD036050. The entire unit is like 10..12ft in length, guessin' at least 15 yrs old?

​​​​​​




I was looking for the coils. But what's bolted and alum. taped I didn't want to mess with, to not create extra work late at night. I did open up this left most section with a radiator looking thingy. It's raditor grills are pretty clean but has rust on the looping copper pipes. Just wondering on a new one would it be good to squirt the copper pipes with oil once a year as a preventative to keep corrosion at bay?


 
  #6  
Old 07-24-20, 09:50 AM
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Yes looks to be a three speed PSC motor. The coil looks fine to me I would say if the system works don't mess with it other then preventive maintenance (oil both indoor and outdoor fan motors filter changes and clean out dust & dirt as best as you can from both coils)
 
  #7  
Old 07-24-20, 11:28 AM
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Electric motors with ball or porous bronze bearings require a non-detergent oil. Do not use ordinary engine detergent oils or common 3 & 1 oils which are also penetrating and have rust solvents. DO NOT USE THEM

My attic GE AC air handler is 53 years old. Replaced original GE compressor unit in 1996.

It is hard to find plain electric motor oil. Here is one I have used for years.

https://www.sidharvey.com/item/F2-32...-Quart-Bottle/

Pictures show all kinds of curd on motor and frame. Either filters are not effective or AC ducts are leaking, may be both. A good case for "preventive maintenance".
 

Last edited by doughess; 07-24-20 at 11:50 AM.
  #8  
Old 07-24-20, 11:47 AM
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Thanx guys. Still have the question-what's the gooey blue stuff in the wire nut and source?
 
  #9  
Old 07-24-20, 11:55 AM
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Do not know what stuff is but "liquid electric tape" might be good protection.

https://www.homedepot.com/p/Star-Bri...104N/206513456
 
  #10  
Old 07-24-20, 01:02 PM
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I also don't know what that gooey stuff is but I have been using This on my fan motors for years. I got mine at Lowes as Home Depot only carries the red can Do not use the red can for electric motors. (I learned that the hard way luckily I was able to fix that goof up but you may not be able to)
 
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  #11  
Old 07-25-20, 10:56 AM
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Many "3 in 1" oils have solvents and rust proofing chemicals that should not be used on electric motors with porous bronze or ball bearings.

I have old, classic can labeled 3-in-One, Household Oil. with words:

LUBRICATES-CLEANS-POLISHES ... PREVENTS RUST AND TARNISH.

I would never use it on motor bearings.

All kinds of stuff is in things labeled " 3 in 1". Buyer be ware.

Plain 20 weight, non-detergent oil can be used.
 
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Last edited by doughess; 07-25-20 at 11:18 AM.
  #12  
Old 07-25-20, 11:29 AM
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3 in 1 motor oil is a mineral based 20weight non detergent. I've been using it for years.

It looks like something spilled in your unit.
That green solution is all over the ductwork in one of your pictures.




 
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Last edited by PJmax; 07-25-20 at 01:49 PM.
  #13  
Old 07-25-20, 01:14 PM
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I would conclusively determine where that blueish oil came from first. We had a unit at work that started making a burning smell when running in heat mode (gas furnace) and we could see very faint smoke near the ceiling in the rooms conditioned by this unit. Turns out the motor was leaking oil onto the hot burner and creating the smoke. A/C guy replaced the motor and all was well again. I realize a lot of motors may not have or leak oil but some do. That system was a Carrier from the mid-90s.
 
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Old 07-25-20, 01:18 PM
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Many "3 in 1" oils have solvents and rust proofing chemicals that should not be used on electric motors with porous bronze or ball bearings.

I have old, classic can labeled 3-in-One, Household Oil. with words:

LUBRICATES-CLEANS-POLISHES ... PREVENTS RUST AND TARNISH.

I would never use it on motor bearings.

All kinds of stuff is in things labeled " 3 in 1". Buyer be ware.

Plain 20 weight, non-detergent oil can be used.

NOT the same stuff. This is specifically for motors: https://www.3inone.com/products/motor-oil/
 
  #15  
Old 07-25-20, 05:39 PM
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@ PJmax Post #12 that is the same stuff I mentioned in Post #10
 
  #16  
Old 08-01-20, 11:10 PM
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Another problem just cropped up.
Now AC unit is turning on and off right away. It only runs for 5 or so seconds then goes off. From reading around this points more towards electrical component problem or the run capacitor. I have replaced capacitors, contactor, etc so I am familiar with such but I am not quite sure where/how to start checking on this unit.
 
  #17  
Old 08-02-20, 03:25 AM
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EDIT:

After 3 hours or so off, turned it back on and it's been running ok for the last 1.5 hours so far.
 
  #18  
Old 08-02-20, 06:13 AM
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Hi, what part of the AC unit is going on and off?
Geo
 
  #19  
Old 08-02-20, 05:24 PM
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Many of the electronic/printed circuit board problems can be found by careful, through inspection of boards. Here is DIY thread on similar problem I had:

https://www.doityourself.com/forum/a...ml#post2853722
 
  #20  
Old 08-03-20, 02:33 AM
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They both seem to go off instantaneously. Can't quite tell which one goes out first
 
  #21  
Old 08-05-20, 10:29 AM
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Q1.
When I turn AC on now it's completely dead, not turning on. The contactor on the outside unit was not engaging. So while AC was turned on, on the TStart I pushed the contactor in the outside unit and unit kicked on and it started running. But the inside unit did not run.

Q2.
I let go the contactor, outside unit turned off. Then I checked the ...what do you call it...signal wire .... I was expecting to find about 27ish volts but there was none. Is there supposed to be 27 volts on this line while TStart is on?


The contactor on the outside unit is getting pitted but it did not engage after turning AC unit on, I had to push it in.



 
  #22  
Old 08-05-20, 12:09 PM
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Hi, itís not a good idea to manually push that contactor in it could result in severe personal injury, anyway , you donít have any power to the control wires at the condenser, can you post a pic of the control board at the AH, you should be able to jump R,Y,G there , fan condenser should start.
Geo
 
  #23  
Old 08-05-20, 04:36 PM
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Thanx for the tip. Not doing that ever again.

I am not sure where to find the board. From my pics above does any one have tips where I can look for the board?
 
  #24  
Old 08-05-20, 05:40 PM
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Since neither the air handler or the condenser is working..... the problem is not out in the condenser.
Based on your earlier pictures your air handler is installed in attic where if it leaked it could cause water damage. Check for a float switch somewhere in the overflow pan or drain line. If that tripped it could keep the system from running.

I highly doubt you have a board problem.

If you have a voltmeter.... check for 24vAC from R to Y or R to C.

 
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  #25  
Old 08-06-20, 08:58 AM
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In old days, bad electric contacts were cleaned with ignition files after first turning off power.

https://www.google.com/search?client...XS0DlUQ4dUDCAs
 
  #26  
Old 08-06-20, 12:40 PM
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Fixed!

There was power in all suggested testing points R to R, R to C.
The offending culprit was the battery contact inside the TS became loose over time. That's it.

Thank you guys!



"Check for a float switch somewhere in the overflow pan or drain line. If that tripped it could keep the system from running."

I don't think I have a float switch. Here's is my setup. What do you think?




 
  #27  
Old 08-06-20, 01:32 PM
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Glad you let us know you got it fixed, it might not be a bad idea to replace that contactor.
Geo
 
  #28  
Old 08-20-20, 09:11 PM
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I have two additional questions...
Q1
Yesterday the AC unit was turned on by my Sonoff wifi unit as usual but it didn't kick in. The cold blinking thing went solid outside unit kicked on but inside unit was making a buzzing sound like it wants to kick on but it wouldn't. So turned it off checked breakers-aok, checked power to air handler-aok but I noticed the door must have vibrated loose. I held in the door switch and unit kicked on right on cue and run fine for the rest of the night after tightening door lock screws.
Today when we came home same thing repeated except door was snug, outside never turned on and inside unit wasn't making the buzz sound. Everything was dead quiet. Waited an hour then decided to replace batteries in the tsat. After cool sign turned constant unit kicked on just fine. Old batteries were new, I installed them barely a two weeks ago and the display was a strong font. Really was this all about batteries?

Q2.
I am thinking I should get a spare capacitor. Below is blower motor cap. I looked up this model and these others also popped up. Are any of them a good equivalent? I have not a clue what to look for in these things, to determine the correct one.

CURRENT CAP


Target replacements












 
  #29  
Old 08-22-20, 08:41 AM
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Ignore previous looong post. I'll make it short.
Inside unit attempts to start, makes a constant buzz for about 10...20 seconds, then the sound goes away. After reading around, this points to a toasted capacitor-have ordered a replacement. While this is happening with the inside unit, observed that sometimes the outside unit would turn on or not at all. When it did, it would run for a minute or three and then turn off. Is this something to worry about or is this behavior being caused by the outside unit realizing the inside unit is not running and therefore it shuts down?
 
  #30  
Old 08-22-20, 11:42 AM
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If the inside blower is not running..... the compressor will overheat but it usually takes more than a minute or two.

We're back to the beginning here..... if your outside condenser is not always starting you need to check the 24v to it.
 
  #31  
Old 08-23-20, 12:27 AM
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while I wait for my order to get here I can use the cap from downstairs unit to TS the upstairs unit. Even though both air handlers are carrier, very identical models, with similar looking blowers, the downstairs cap is rated 5mfd while the now toasted upstairs cap is a 7.5mfd. Not wanting to risk messing up anything my Q is will the former cap (5mfd) be able to power the upstairs unit?

Here is downstairs airhandler


Upstairs unit needing T/S

 
  #32  
Old 08-23-20, 01:41 PM
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Replacing the blower motor cap fixed the same problem for me a couple days ago. I was lucky and had ordered one when I noticed the blower was taking longer to spool up. Not a bad job. Be sure to cut power to the unit and de energize the old cap.
 
  #33  
Old 08-26-20, 08:18 AM
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Slotted in new cap, everyone is happy at the ranch
 
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