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  1. #1
    Join Date
    Aug 2011
    Location
    USA
    Posts
    32

    Trane Heat Pump with communicating thermostat

    I'm not sure if I'm in the right forum area. I worked on a heat pump air conditioning unit the other day and the communicating control board was flashing a code saying it was on high pressure lock out. After checking all the basics nothing showed obvious as to what was the problem. I disconnected the power supply to the control board to see if it would reset and it did. I decided that it was the control board itself and replaced it. The person did not have the problem again before I changed it but just to be sure I replaced it anyway as it is under warranty. What do you think the problem is???

  2. #2
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    1,058

    I would look

    at all the things that could cause a high pressure situation and go from there. Did you put gauges on the unit? How clean is the outdoor coil? Etc, Etc, Etc.

  3. #3
    Join Date
    Aug 2011
    Location
    USA
    Posts
    32
    The coils looked clean and the unit is no more than a couple years old. I noticed for a brief moment the compressor kicked on before the fan which suggested there was a problem with the fan but it checked out fine. The other tech was checking the inside unit and he didn't find any problems there. I did not put the gauges on it because I pulled the power to the control board and it reset with no problems. I'm pretty sure it's not overcharged. The person has not called back with any problems. I'm pretty stumped on this one what do you think some of the most common causes would be. It's a Trane a/c heat pump with the communicating board.

  4. #4
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    1,058

    Did you

    operate the unit in both stages? What is the model # of the outdoor unit?

  5. #5
    Join Date
    May 2009
    Posts
    612
    Quote Originally Posted by GSC View Post
    The coils looked clean and the unit is no more than a couple years old. I noticed for a brief moment the compressor kicked on before the fan which suggested there was a problem with the fan but it checked out fine. The other tech was checking the inside unit and he didn't find any problems there. I did not put the gauges on it because I pulled the power to the control board and it reset with no problems. I'm pretty sure it's not overcharged. The person has not called back with any problems. I'm pretty stumped on this one what do you think some of the most common causes would be. It's a Trane a/c heat pump with the communicating board.
    Always put your gauges on a system. You cannot begin to troubleshoot without superheat, subcool, temp diff across a coil, amp draws, static pressure and capacitor readings.

  6. #6
    Join Date
    Aug 2011
    Location
    Ohio
    Posts
    53
    Quote Originally Posted by ChaseAir View Post
    Always put your gauges on a system. You cannot begin to troubleshoot without superheat, subcool, temp diff across a coil, amp draws, static pressure and capacitor readings.
    Not to be ignorant, however in school we were taught that the last thing a technician should do is put the gauges on. Rule out all other problems because you always lose a little refrigerant each time you put the gauges on and off. However in the situation the OP had I would have put the gauges on to see what the high pressure side was doing since it locked out on high pressure. However before I did that I would have checked the run capacitor on the condenser fan motor, checked to see if the fan turned easily, and I would have read the current on the condenser fan and checked it against the RLA to see if it was running harder than normal.

    I am pretty new but I believe that this was probably caused by the fan not starting once and then the next time it started after you reset the board. I was on a service call once where the outdoor unit was not running. Turned out the compressor would start but the fan would not and it would cut out on high pressure. After checking the cap and windings I swapped the terminals and forced the fan backwards for a second and it loosened it up, after that it ran forward but took a bit to start. The current was about an amp higher than normal so we lowered the thermostat and let it run continuously (because we were afraid it wouldn't start again) until we could get a replacement motor a few hours later. So I guess my point is motors with worn bearings could start intermittently for several reasons.

    I'm just thinking out load really.

  7. #7
    Join Date
    Oct 2008
    Location
    Nashville ,TN
    Posts
    337
    Yes dirty dryer will effect super heat and subcooling. Some people mistake bad txv and it was plugged liquid dryer. Best thing is to keep reading and enjoy fixing things. You seem to care so in my book your ahead of alot.

  8. #8
    Join Date
    Oct 2008
    Location
    Nashville ,TN
    Posts
    337
    Wow just noticed that my phone was changing my spelling lol. Driers not dryers. System Diagnostics and Troubleshooting Procedures very good book on refrigeration. Not very expensive, got it off amazon some years back. It shows problems and the kind of symptoms that come with those problems.

  9. #9
    Join Date
    Apr 2003
    Location
    Columbus Ohio
    Posts
    96
    it probably got switched over into heat mode on accident

  10. #10
    Join Date
    Oct 2008
    Location
    Nashville ,TN
    Posts
    337
    ive had something close to your problem could be a weak run capacitor, have you checked the play in the outdoor fan shaft , sometimes when bearings go bad it runs fine while youre their and when you leave locks up.It shouldnt move alot from left to right .

  11. #11
    Join Date
    Aug 2011
    Location
    USA
    Posts
    32
    I cant remember the model#. If I get a call to go back there I will have to check the run capacitor. The unit is pretty new so I dont think its the fan but I didn't check it. It was one of those situations were the problem was fixed quickly and then I moved on to the next call. I'll have to remember to ask the other service tech that was with me on some of these questions. My description is kind of vague. I was thinking it might have been the sensor malfunctioning but I'm not to firmiliar with these kind of units with communicating conrtol boards. Do any of you guy's know were I can get some literature on these type of systems?

  12. #12
    Join Date
    May 2009
    Posts
    612
    Trans has a service manual on them. High superheat can cause a reciprocating compressor to go into thermal cutoff occasionally.

  13. #13
    Join Date
    Aug 2011
    Location
    USA
    Posts
    32
    I guess if Trane tests the control board I'll know for sure if that wasn't the problem. I'm a FNG in this field and I was with another service tech training me. I definitely agree on putting guages on at all times that will be kept on the top shelf when I get out on my own!!!!!!!

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