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  1. #1
    Join Date
    May 2006
    Location
    Enfield, CT
    Posts
    37

    Carrier 38AKS012-501 misbehaving?

    I'm a mostly residential Heating and A/C contractor. I'm in the northeast so A/C is only for a few months and not an everyday event. A fellow technician went on vacation and he asked me to help him if any service calls came in. Of course it was the hottest two days in this area with high humidity and I get slammed with other calls. Then I get a call from a Church. No A/C in the meeting area. So I take of to the call. The Air Handlers are running but only very warm air is coming out. I craw up the access stairs and just about fell back in due to poor setup at the top. Who approved this crap. Well that's for another thread. Checked obvoius things in the catwalk area. Filters are clean etc. I go back outside. It's now 105 heat index per the weather man. The uit will start every 10-15 minutes for about 3 seconds then stop. The fan won't get up to speed and the contactor de-energizes an both the fan and compressor stop. Refrigerent piping very hot. Checked the fan windings 3 phase 220 had 6 ohms accross all three windings. Now I don't work on Carrier very often and especially commercial. I'm licensed for Comm and Res. and had the schooling back in the 80's but I don't see them enough. I checked the Voltage coming in at all legs OK. Fuses O.K. Contactor getting full juice. But the fan and compressor would both only run for 3 seconds. I had other calls and they only use this area once this weekends so I turned the breaker off for the weekend. I returned today in the AM. Measured the winding again, hooked up gages. Turned unit on at breaker (outside) and the unit took off. The pressures were as follows Low Side at 36 deg. High side at 179psi 95 deg. WB 60 deg. OD amb 68 deg. SH 22 deg SC 15 deg. Inside cond 72 degrees. The ceiling is about 20 cathedral. Is there something I'm missing here? Unit still running. Looking for some answers as to why this unit would cycle on high pressure without the fan running. The contactor would pull in for 3 seconds the release. Shouldn't the fan be running even if its off on high pressure or low pressure? I advised the Property Manager to find a Carrier specialist since there are 10 units all Carrier and in different denominations. I'm just trying to get some insight here so I can truly back up my good friend when he's trying to get some Family time i that is way overdue.

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Go to the PDF available at this link:

    http://www.xpedio.carrier.com/idc/gr...f?SMSESSION=NO

    Scroll down to Page 8 and study the control circuitry in Figure 6. Examine everything that can make or break the circuit to the contactor coil. High and low pressure switch, time delay relay, compressor lockout relay. It will then become a matter of determining which component is opening the circuit once the contactor energizes.

    When you returned today in the AM, you found you could run the unit without it misbehaving. What changed? You noted an outdoor ambient temperature of 68 degrees. On your previous visit you noted that conditions were hot enough to cause a local weatherman to indicate the heat index as 105 (not real useful information, as the condenser does not care what the "heat index" is).

    Why the difference between then and now? If you study how this condenser is put together, it has a double row coil. The PDF link I gave describes how to separate and clean these coils. I'll bet'cha a dollar to a donut these coils have never been split and there's a wool blanket of crap between the two coil sections, causing the high pressure switch to trip. There may be a non bleed TXV at the evaporator, or possibly a liquid line solenoid, so during the off cycle the pressures do not equalize. They only diminish slightly, enough to allow the high pressure switch to reset, but not enough to allow the unit to run for a longer span before it trips out again.

    The contactor controls both the compressor and condenser fan motor. This system has a semi-hermetic compressor, but does not show, at least on the PDF, that it has an oil pressure switch. Symptoms you gave do not indicate low oil pressure, anyway. If such a switch existed, typical Carrier logic allows compressor to run long enough to establish sufficient oil pressure before returning low pressure switch to the circuit to open circuit to the contactor, stopping the compressor if oil pressure had not built up high enough in the allotted amount of time. If this system DOES have an oil pressure switch, you need to check oil pressure. I'm not led to think your problem is there, since the cooler day would tend to aggravate a low oil pressure problem, not alleviate it.

  3. #3
    Join Date
    Apr 2001
    Posts
    669
    Quote Originally Posted by shophound View Post
    Go to the PDF available at this link:

    http://www.xpedio.carrier.com/idc/gr...f?SMSESSION=NO

    Scroll down to Page 8 and study the control circuitry in Figure 6. Examine everything that can make or break the circuit to the contactor coil. High and low pressure switch, time delay relay, compressor lockout relay. It will then become a matter of determining which component is opening the circuit once the contactor energizes.

    When you returned today in the AM, you found you could run the unit without it misbehaving. What changed? You noted an outdoor ambient temperature of 68 degrees. On your previous visit you noted that conditions were hot enough to cause a local weatherman to indicate the heat index as 105 (not real useful information, as the condenser does not care what the "heat index" is).

    Why the difference between then and now? If you study how this condenser is put together, it has a double row coil. The PDF link I gave describes how to separate and clean these coils. I'll bet'cha a dollar to a donut these coils have never been split and there's a wool blanket of crap between the two coil sections, causing the high pressure switch to trip. There may be a non bleed TXV at the evaporator, or possibly a liquid line solenoid, so during the off cycle the pressures do not equalize. They only diminish slightly, enough to allow the high pressure switch to reset, but not enough to allow the unit to run for a longer span before it trips out again.

    The contactor controls both the compressor and condenser fan motor. This system has a semi-hermetic compressor, but does not show, at least on the PDF, that it has an oil pressure switch. Symptoms you gave do not indicate low oil pressure, anyway. If such a switch existed, typical Carrier logic allows compressor to run long enough to establish sufficient oil pressure before returning low pressure switch to the circuit to open circuit to the contactor, stopping the compressor if oil pressure had not built up high enough in the allotted amount of time. If this system DOES have an oil pressure switch, you need to check oil pressure. I'm not led to think your problem is there, since the cooler day would tend to aggravate a low oil pressure problem, not alleviate it.
    Due to the CLO, just one trip of the LP Safety or HP Safety would lockout the compressor until reset. He did not see the CLO trip.

    I have found a common mistake made by residential techs that are new to commercial. Many of them do not know that there is a difference between the 230 volts that they see everyday and the 208 volts that they never see. Also, available voltage during hot days drops down lower than available voltages during milder weather. And finally, the control voltage transformer that comes with the condensing unit comes factory wired for 230 volts (see diagram on Page 8) which will work on 208 volt systems until a warm day comes.

    If the control transformer is on a 208 voltage system and comes from the factory pre-wired for 230, there is going to be a problem in warmer weather due to the lower voltage available.....but will not be noticeable in milder weather. If this is the case, the primary input (orange and yellow) needs to be changed to red and yellow. Again see the transformer wiring in the diagram on page 8.

    Jabs

  4. #4
    Join Date
    Mar 2005
    Location
    Fort McMurray, AB
    Posts
    113
    whats your lowside psi ?
    could be a few things
    unit could be low on gas and the low pressure opening and closing
    but 36 deg suction line, u may have a airflow problem.

  5. #5
    Join Date
    Apr 2001
    Posts
    669
    Quote Originally Posted by desroches View Post
    whats your lowside psi ?
    could be a few things
    unit could be low on gas and the low pressure opening and closing
    but 36 deg suction line, u may have a airflow problem.
    Due to the CLO, just one trip of the LP Safety or HP Safety would lockout the compressor until reset. He did not see the CLO trip.

    Jabs

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Quote Originally Posted by Jabarco View Post
    Due to the CLO, just one trip of the LP Safety or HP Safety would lockout the compressor until reset. He did not see the CLO trip.

    Jabs
    True. Toward the end of composing my post, I also realized this. That's what made me think re: non-bleed TXV. LLS would be energized for a cooling call and if system tripped the energized LLS would allow the system to equalize. Even so, any high pressure trip is going to lock out the compressor.

    From what I could discern from the OP, he had to shut the power off to do his ohm check of the compressor windings. When he did this, the compressor lockout control would be reset once power was restored. Upon power-up the compressor would attempt to start, then hit the limit and trip off again. Maybe the OP then made the connection that whenever he cycled power, he could get the unit to start, albeit briefly.

    Seems to me if it was a low control voltage issue, the contactor would chatter. Or it is doing something funky to the time delay logic. I would indeed verify if the transformer is wired correctly, and if so then look for the fault elsewhere in the circuit. I would also want to return when outdoor conditions are similar to what caused the the thing to misbehave the first time. He needs to be able to duplicate the conditions leading to the problem to prevent a callback.

  7. #7
    Join Date
    Mar 2005
    Location
    Fort McMurray, AB
    Posts
    113
    Quote Originally Posted by Jabarco View Post
    Due to the CLO, just one trip of the LP Safety or HP Safety would lockout the compressor until reset. He did not see the CLO trip.

    Jabs

    i never caught that. i am also thinking now that i would have a look at the supply transformer voltage, also have a look at the time delay.

  8. #8
    Join Date
    May 2006
    Location
    Enfield, CT
    Posts
    37

    Thanks or the info!

    Thank you for the instruction attachment. I didn't have access to it on the job. Also the timer is disconnected and the origional transformer is also disconnected. I found out they have been having problems with all the contractors that have serviced this acct. The guy I'm helping out just fixed another unit with my help last week at the same place but he too doesn't want to get involved in this rats nest. We found soldered joints on compressor changeouts. I noted RTV on another unit while I was there. So I'm thinking that this place is a nightmare. I'm thinking it's the liquid line selinoid that may have hung up. I think the design of the circuit to drop out the fan when there is a high pressure or low pressure condition seems strange. Thanks for all the help with this one. Next time I'll try to be more thorough before I throw the switch and let it cool down.

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