Compressor Doesn't Start Reliably (tech claims theormstat is problem???)
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  1. #1
    Join Date
    Jun 2005
    Posts
    19
    Hi folks I need some input from the forum. This is my first posting though I have lurked here a while.

    Late last week I noticed that my downstairs AC (technical details provided a the end of this post) was putting out air at the ambient inside air temapture. I went outside and instantly noticed that while the blower motor in the condesor was running the compressor was not (it is a reciprocating compressor that makes an obvious though not loud noise when running). A also felt the suction line and it was the ambient outside tempature. So the inside and outside blower motors were on but the compresser was not. I sat there and "watched" it for a while and all of a sudden the compressor starts to groan and starts up but sounds like it is struggling for about 10-15 seconds. Further experimentation shows that the compressor will always start if the time between the last time it was run and the next time it is started is 10 or more minutes. Any less time than that and the compressor will start around 65-75% of the time (often making some odd protest noises). When the compressor doesn't start the outside and inside blower motors run and the compressor does eventually start with some protest about 5-10 mins. later. Once on the compressor stays on until the thermostat shuts everything off. My Chronotherm III thermostat has a 5-6 minute delay built in but that does not appear to be sufficient.

    So I call the contractor I have used before to replace the upstairs HVAC equipement (and been happy with) and the earliest they could come out was today (Tuesday). Which is fine since I know they are busy. I turn off the downstairs AC since leaving a sometimes stalled compressor presumably powered seems like a bad idea to me.

    So the tech comes out today and unfortunately I am out of town so my wife speaks with him. He says the compressor has a cracked valve and will "eventually" need to replaced (this was indicated by the refrigerent pressures being off as the low side was high and the high side was low) but that the intermittent compressor operation is due to our Thermostat and that is what needs to be replaced. He told my wife that it was okay to operate the unit and that there was no need to replace the compressor until it died completely. It does cool the house fine, though I did notice that as a heat pump it was less effective this winter than before (it seemed to run much more often and for great lengths of time between cycles).

    So my questions are:

    One I don't believe that the theormostat controls the compressor directly so I do not see how that can be the main problem. It is a high quality Chronotherm Honeywell installed about two years ago. If the thermostat was the problem, wouldn't it impact the inside and outside blower motors as well?

    Two worrying about my theormstat when I have a "sick" compressor seems to me like a mechanic trying to sell me new tires for a car that has a dying engine :-).

    Three I don't believe it is safe for my wife to run the AC with a compressor that is may burn itself out if it doesn't start.

    Four the tech did mention that there is generally a 10 year warranty on compressor from Trane and this unit is currently 8 years old. How do I go about checking on this as the unit was installed prior to my purchase of the home and I don't have the paperwork.


    A bit about my equipment, the condesor unit is Trane SEER 10 heat pump (I think XL1000 but I am out of town so cannot check). It was manufactured in the 1st half of 1997 and appears to have been installed on 7/17/1997 due to this date being scrawled on the back of it. The inside unit is a Trane gas furance circa 1986, original to the house. I assume the evaporator is original to that time but I am not sure. Based on the upstairs unit, the orginal heat pump was pobably an old GE from 1986. The thermostat is a contractor grade Chornotherm III (NOT the cheapened Home Depot version) that was installed about two years ago.

    Sorry for the length of my post and I appreciate your advice.

    Miles

  2. #2
    Join Date
    Apr 2005
    Location
    San Luis Obispo County, CA
    Posts
    215
    You could have a number of problems, and the compressor could be going bad. But as far as the thermostat causeing the compressor not to start properly, as long as the delay is working, I don't think so.

    Sounds like you need to find a different tech.

  3. #3
    It appears that your systems pressures are not equalizing fast enough before the next cooling cycle is initiated ; this makes the compressor start under an elevated pressure instead of an equalized pressure. A properly sized Compressor Hard Start Kit would be the remedy for this scenario. Trane will offer one as an Option for your particular model unit -- i would obtain another Service Tech to give you a second analysis as changing out the thermostat is not the answer for the compressor laboring trying to start. All the thermostat does is send a signal to the A/C's contactor and after that, the unit and its internals take over.

  4. #4
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    first if the compressor isnt starting up it may need a hard start kit. since the valves are going bad as stated rather then waiting for it to just burn out and cause more problems and it is under warrenti have them replace it now.
    worn valves will cause you to spend more to cool your house and as it gets hotter out the more chance it will give out and not pump at all. if it burns out there is a strong chance accid will get into the system and more problems. get another opinum and replace it

  5. #5
    Join Date
    Jun 2005
    Posts
    19
    Thanks guys! I was coming to that conclusion but I wanted to make sure I wasn't losing my mind. I'll call another tech. I am assuming I should leave the AC off till we get it looked at? At least if I don't want to damage my compressor any further?

    Miles

  6. #6
    Join Date
    Jun 2005
    Posts
    19
    Originally posted by tinknocker service tech

    worn valves will cause you to spend more to cool your house and as it gets hotter out the more chance it will give out and not pump at all. if it burns out there is a strong chance accid will get into the system and more problems. get another opinum and replace it
    That was my opinion when I heard it was likely bad but the tech appearhently didn't think it was worth doing ???. I am a strong believer in fixing problems earlier rather than later. Pay some now or more later :-). Even if I have to pay for it myself I am not going to leave that compressor there if a second tech tells me it is dying.


  7. #7
    Miles, Yes...if at all possible., leave the A/C unit off whenever you believe it to be malfunctioning. If you absolutely need to run it, then, make very certain the Compressor inside starts up on its first attempt ... which may require you using it at far greater intervals ; and, if it isnt cooling after its been on for 5 minutes, then, its time to keep it off till a qualified Service Tech looks at it. Secure a qualified 'Trane' Service Tech because they undergo specific training on Trane equipment and will typically diagnose it right the first time.

  8. #8
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The XE1000 heat pumps built in 1997 had a 5 year compressor warranty.

    The difficulty starting could be due to a number of problems, none of wich have anything to do with the thermostat in your case.
    It could be something as simple as a weak run capacitor. If the capacitor is weak enough, in addition to the compressor having difficulty starting, it could even cause the system to run with higher than normal suction pressure and lower than normal head pressure.
    There needs to be more diagnostic work done before condemning a compressor than just looking at the pressures.

    You need to get a qualified service tech out to look at it. It doesn't sound like the one you got really knew what he was doing...

    If your compressor does have bad valves, they didn't just fail on thier own, something caused it. The cause needs to be found and corrected.
    If more government is the answer, then it's a really stupid question.

  9. #9
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    Just going to through my 2 cents in. Yes, you need another service tech. You may have like was stated a few times, a few problems. The bad valve diagnosis on the compressor by a un qualified tech, could be a bad (leaking) reversing valve It may be bypassing giving you the high back and low head, causing the compressor to run hot. No sense in telling you how to check this, he should know! If the compressor is to be changed, replace the reversing valve, unless a qualified person like most on this forum, can say its the compressor, I would replace the valve also, period.

  10. #10
    Is that post available in a Cliff's Note?
    Hey cockroach, don't bug me!

    www.AskTheDiceman.com

    www.TheColdConspiracy.com

    www.Pennwood-HVAC.Com

    Bring Em Home....

  11. #11
    Join Date
    Jun 2005
    Posts
    19
    Hee hee, sorry about that :-). Cliff Notes version:

    1. Compressor doesn't always start with rest of system.
    2. Called tech.
    3. Tech comes, spends much time on cell with unknown party presumably asking for assistance in diagnosis or perhaps setting up date with girlfriend.
    4. Diagnosis is "weak compressor but starting problem caused by thermostat."
    5. Suggested action from tech ignore compressor replace thermostat???

    :-)

    P.S. Thanks to all for all the advice. I am going to call somebody tomorrow who sells/repairs Tranes.

  12. #12
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    Originally posted by secstate
    Hee hee, sorry about that :-). Cliff Notes version:

    1. Compressor doesn't always start with rest of system.
    2. Called tech.
    3. Tech comes, spends much time on cell with unknown party presumably asking for assistance in diagnosis or perhaps setting up date with girlfriend.
    4. Diagnosis is "weak compressor but starting problem caused by thermostat."
    5. Suggested action from tech ignore compressor replace thermostat???

    :-)

    P.S. Thanks to all for all the advice. I am going to call somebody tomorrow who sells/repairs Tranes.
    this says it all call a real tech and find out what is truely wrong

  13. #13
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    My two cents worth (unfortunatly Canadian Cents so probably only 1.5 cents worth). No way a thermostat will cause the indoor blower, condensor fan but not the compressor to start. Sounds like your tech doesn't know his ass from a hole in the ground. Check the capacitor, check the reversing valve is opening fully, check for start up amps, although if it is not blowing the breaker it is obviously not pulling more amps on start up than allowed. I have a strong suspicion that the start cap is not working correctly. Before changing out the compressor try changing the capacitor. It is a much cheaper fix than changing out the unit.
    "Go big or Go Home"

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