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It Always Happens At Night


Trouble, that is. Murphy is surely a vampire! Murphy never sleeps patiently through the night, punches the time clock at 8AM on a weekday and then goes about his mischief. Nooooo… He has to work at night. Even better, on a Friday night when repair parts won’t be available for days. Murphy is particularly fond of cutting up with air conditioning at night.

Take tonight. A storm front is moving in and the air is heavy with humidity and heat. The kind of night where you sweat sitting still. Naturally that would be the time for my central air conditioner to take a powder.

The Enemy
The enemy

I’d known for a few days that this l’il buddy was needing some attention. It had frozen up a few days ago. That’s almost always a symptom of low refrigerant, assuming the obvious things like clogged filters have been checked. All my refrigeration gear is still back in Cleveland in my warehouse so I kept my fingers crossed until I could make a trip out of the mountains. Lot ‘o good that did me.

Along about midnight it started getting REAL hot in here. I checked a vent – no flow. Frozen up again. Now there’s one very nice thing (to go along with all the un-nice things) about a heat pump. When the evaporator freezes, just flip the thermostat to heat and let it thaw itself. That I did and then ambled around the cabin to watch a veritable river of water flow out the condensate line. So far so good.

After the major thaw is accomplished with the heat pump, I normally turn the compressor off and let the fan blow for awhile. That thaws the ice that isn’t immediately heated by the heat pump. I turned the heat pump off, turned the fan on and noticed that I still heard the unit running. Sure enough, when I walked back outside, the compressor was humming merrily away.

This time I turned everything off and went back outside. Yep, still running. *sigh*. Without even looking at the clock, I knew that I had another night of fighting Murphy ahead of me. Sooooo… I gathered up my tools and headed out.

I took the covers off the unit to access the control box. Just for grins, I gave the box a good THWACK. Shazam! The compressor turned off. A closer look showed this to be the culprit

Contactor 01

This is the main compressor contactor. An even closer look shows this

компютри втора употребаContactor 02

See the area with the light yellow circle overlaying it? That is one of the contacts. See how burnt it is? That cheap piece-o-crap had welded its contacts together. When the thermostat told it to turn off, it refused. My thwack broke the weld. Also fairly evident in that photo is how badly the contacts had overheated. Typical of the crap that Rheem uses.

What was happening was that when the thermostat turned the unit off, the air blower stopped but since the compressor contactor was welded shut, it kept running. It froze whatever water (condensate) that remained on the evaporator. When the thermostat called for cooling again, part of the evaporator was blocked by ice. The cabin cooled more slowly this time and when the thermostat turned the cooling off, the cycle repeated. Each time a little more of the evaporator froze up until not enough air could flow to cool the cabin. Then the whole system ran continuously and I got hot!

I headed back to the basement but quickly remembered that all my refrigeration stuff is still in Cleveland including my supply of spare contactors. Damn. I rummaged around the cabin and found one of mom’s old nail files. I trimmed it down and crammed it in there as best I could to sand down the worst parts of the burned contact area. Hopefully it’ll hold until I can go to town tomorrow to get a replacement. A much heavier duty replacement.

Freon Shortage

There still remained the problem of the unit needing refrigerant. My supply of refrigerant is also still in Cleveland. I knew that the unit would freeze up again if I left it as it was, especially with humidity dripping out of the air. Too hot to go without air conditioning. Soooo.

A little known fact is that propane is an excellent refrigerant. It even has its own “R” number. Even less well known is that propane behaves almost identically to R22, the refrigerant used in home air conditioners. Soooo.

I rummaged around and found my disposable propane cylinder to 1/4″ flare valve adapter. I also found a disposable cylinder of Coleman propane. I use this because the propane is MUCH cleaner and dryer than the propane that comes in your gas grill tank. I charged about a pound of propane in the system. The cold side temperature dropped, the refrigerant pressures got right and all is well with the world. I’m just keeping my fingers crossed that the ice didn’t damage the evaporator and cause a refrigerant leak.

Here I am about 3AM, the sweat drying on my brow and the cabin cooling off nicely. I’ll be running the fan control in the “ON” position instead of “AUTO” so that if the contactor sticks again, the cabin will simply get cold instead of the unit freezing up. I’ll grab a nap and then it’s off to the big city to buy parts.

Foiled you again, Murphy!

Posted by neonjohn on June 4th, 2008 under HVAC

4 Responses to “It Always Happens At Night”

  1. Lee Bray Says:

    Hey John

    Do you have a photographic memory? You never cease to amaze me with all of the things you know and do.

    Lee (Jacksonville, Fl)

  2. Ralph Marotta Says:

    Hi John
    Enjoyed reading and realizing that Murphy picks on others besides me.
    But after diagnosing and correcting the cause of your freeze-up problem, I’m a little confused as to why you decided to add gas to the unit.
    If additional refrigerant was needed, I think it’s a safe bet that there IS a leak in the system…..


  3. neonjohn Says:

    Hey Ralph,

    Even after fixing the sticking contact, the suction side pressure was low according to the pressure vs ambient chart stuck to the inside of the rig. Plus I could hear bubbles in the capillary tubes with my mechanic’s stethoscope. An additional clue was that the evaporator exit temperature was higher than I like to see.

    I charged until I got solid liquid sounds at the capillaries which happened to coincide with the suction pressure matching the chart.


  4. DrRick Says:

    Hey John,
    I think I found your blog through a posting of yours on a ham radio or boatanchor reflector.
    It was referred to as “the best blog on the internet”
    I have to agree that its one of the best!
    My Rheem piece of crap central air unit died a few years ago. I noticed that it was icing up, so I asked my kids to leave it off until I could get someone to recharge it.
    So, of course, the next day the breaker was blown. I had someone look at it and he said the compressor was shorted.
    Do you have any thoughts on this? Also, do you know of a cheap place to get a compressor?
    The heat never used to bother me much, but with the health problems I’ve developed the heat is unbearable! I need AC!, but the disability check doesn’t go very far.

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