Monday, June 15, 2015

Channeling my inner "Mostly Cajun"

Our forty year old central air conditioning unit is on the blink.  It did not want to cycle on.  But once on, it did not want to cycle off.  Sounded like a relay or contacts to me.

I asked Mrs ERJ to hold off on calling our HVAC guy.  I wanted to take a look.  Note:  Power was dumped at the breaker.
Hmmm! It is a wee bit hot and muggy out here.  The lens fogged up.  I will try again in a few minutes.
Ok, there we go.  Evidence of animal nesting (mostly cleaned up before this shot).

Circuit open

Circuit closed.  Note, stayed stuck Closed when screwdriver was removed.
A third of a can of contact cleaner took care of that issue.

Top still shiny and wet from contact cleaner.  Rodent turds and hair washed out.  Yuck!  Moves freely in both directions and does not stay stuck-closed.
That explains it not turning off but we are still missing the reason for it not cycling on repeatably.

Well, it is a no-brainer to tighten all of the screws on the lugs that connect the wires to the device.  While doing that I bumped a wire that wiggled too much.  The female terminal was in three pieces.

Bright blue in center of frame is the replacement for a 1/4 inch, female terminal that had fragmented.  The only contact between the wire from the orange 24V control wire and the contacter was due to from the spring of the wire.  Duct tape was added to a chafed region on the orange wire leading away from the contacter.
I have never seen a tin-plated, brass terminal disintegrate like that.  That is our probable cause for the contacter not closing when the thermostat said "AC ON".  The contacter could not get enough juice across that causal contact.

I did not like how close this ground wire connection was to the contacter.  The little metal tab immediately to the right of the yellow wire-nut is supposed to move up-and-down.  I rerouted the wire so it would never contact and impede the contacter tab.
Only two extra parts!  That is pretty good for me.
Rodent poison will be placed inside the cabinet and the entry holes found and closed off.

I am waiting an hour for the contact cleaner to fully evaporate before cycling the AC unit.  I have my fingers crossed.  I may have saved us a couple of hundred dollars.


  1. Im sure you did. And it IS a tad unusual for a contact to fragment like that, especially just ONE of them... Material failure?

    1. It is a puzzler. I don't know if brass is subject to hydrogen embrittlement.

      I think fatigue played a factor. Compressors generate much vibration.

      Based on the discoloration of the spade (male) It may be that the terminal was not completely seated on the spade.

      I will be OK if this is only a temporary fix. I will be happy even if it fails in forty years.

    2. Here we go: Page six.

      Stress corrosion cracking of brass in the presence of ammonia. Decomposition of urine creates ammonia. Maybe our little biological contributed to this failure.

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  3. A good, competent A/C man is a joy to know.

    1. Getting the A/C back on-line did wonders for my popularity around the house.

  4. Urine is very corrosive- You might consider looking at the contacts as well, to see if they are badly pitted.

    1. Good to know! They are almost impossible to inspect due to location but I can take a couple of swipes at them with an emery board as an insurance measure.

    2. For auto points, it was recommended to use a steel file so no abrasive would embed. Do not know if that is necessary with these.


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