4 Bad Boards in 4 Days! (a new record)


Yes, the title of this post is exactly what a contractor had done on a unit — replaced 4 boards in 4 days. I finally got the call from the owner of the building, who was very frustrated and upset with our product because the unit was only in it’s second cooling season and they had changed the unit out to avoid a lot of problems.  Now they can’t get cooling and the contractor is telling them we have a “bad bunch of boards”!  After calming the building owner down and assuring him that we are not having a “run of bad boards”, I have him call his contractor and tell him that I will meet them on the site and we set a date. The building owner agrees.

Now, how many times have I posted that, in most cases, there is nothing wrong with the board?  Well, this jobs is going to prove that point again — it usually is not the board! This morning, I meet the contractor at the site, we go up on the roof, and he is telling me all that he has done and that it has to be bad boards.

We start our diagnostic.  First we check the voltage into the unit and it is reading 212 VAC (3 phase system).  We look at the transformer and it is still on the 230 VAC tap. We have our first problem — this causes low secondary voltage — 23.1 VAC with no load — to the control and safety circuit.  We move the power wire to the 208 VAC tap on the transformer and we now have 26.3 VAC secondary voltage.  This should help solve some possible issues.

We then go to the board, the thermostat wires have been removed, and we want to turn on the cooling.  Since the thermostat wires were still off the board, we leave them off to see what is happening “locally” in the unit.  I get out my trusty jumpers and place them between R, Y, and G to turn on the cooling.  I get a flash code 2, which is good, meaning the board is in a 5 minute anti short cycle mode.  I bypass that with the reset button and I get the flash code 7 and then back to the flash 2.  Flash 7 is the board saying that the suction line freeze safety is open.  We ohm out the freeze stat and t is closed.  We disconnect the freeze stat from the board and jump it out on the board, recycle the power to reset it and still get the flash 2 followed by the flash 7.  It is just this scenario that the contractor has been saying occurs and why they have been replacing the boards.

So, did they have 4 bad boards?  What else should they have checked? The board currently in the unit has the correct voltage to it now that we reset the power side of the transformer. We have eliminated a possible thermostat problem by disconnecting it off the board — so what else could it be?

Here is where the old analog meter becomes a valuable diagnostic tool.  With the meter attached to the 24 VAC power into the board, as soon as the time delay passed or was bypassed, the 24 VAC dropped down below 15 VAC, the board went into a lockout and started the sequence all over again.   We did this a couple of time to convince the contractor that something else was causing the lockout and the board was doing what it was designed to do.

The first thing we disconnected was the compressor contactor since that probably has the largest current draw of any controls attached to the board.  WE recycle the power again, watch the meter, the time delay passes and the voltage stayed constant and the needle on the old analog meter never bounced.

We were pretty sure the problem was a bad 3-pole contactor for the compressor at this point. The blower motor came on fine so it wasn’t that circuit.  there were no flash codes on the board other than a normal heart beat meaning everything was fine.  To verify, we reattached the compressor contactor to the board and as soon as the delay passed, it went into the lockout.  We put in a new contactor and everything now worked.

A few points to be taken from this hopefully —  (1) it usually is not the board —  (2) an analog meter is still an excellent diagnostic tool — (Most digital meters do not react quick enough to a voltage drop like this or to a “bouncing” switch). When we were done, I further explained to the contractor that the reason the flash code 7 showed up is because it was the “shortest” run of wire for the safeties. The other safeties were in the condenser section (high & low pressure switches), so the board saw this open (probably only momentarily) before the other switches and flashed it’s code. That is why, even when he jumped it at the board, he still got that flash code.

Hopefully, you readers have learned something valuable today? Us “old timers” will never get rid of our Simpson 260’s or even our cheap pocket analog meters. They are too valuable in making this type of diagnostic. Digital meter are great but for certain things you can’t rplace the analog meter.   Also, hopefully I have shown again, it usually is not the board!. By the way, the building owner was happy that we solve his problem and he had cooling again!

Advertisements

About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
This entry was posted in HVAC Tech Support and tagged , , , , , , , , , , , , , . Bookmark the permalink.

9 Responses to 4 Bad Boards in 4 Days! (a new record)

  1. Very interesting and certainly good troubleshooting on your part. It would be interesting to know why the board did not get a low voltage lockout and why the 24 vac transformer was so loaded by the contactor that it reduced voltage but did not blow a fuse.

  2. mike says:

    Interesting and informative reads thanks

  3. Kim Tebbs says:

    We have had the same issue with three different york rtus in less than a year. You make it sound like it is an obvious troubleshooting sequence. I’m here to tell you it is not. Who would think that a low resistance on the coil side of a contactor would cause a freeze stat error at the board? York has a problem they should address with this issue in my opinion. Thanks for the article though, it has helped us with some very frustrating service calls.

  4. Again thanks for the article as we are experiencing the same on 3 YORK RTUs. ZF150. Although we pride ourselves on thorough troubleshooting, Ohming the contactors did not cross our minds as we were too focused on the error codes being presented to us. This needs to be addressed by York.

    • The contactor issue was resolved back in 2014. If you are experiencing this on new units, you should contact your local York distributor and have them notify the factory with a product report.
      Glad my post was able to help you solve your problem.

  5. Mike R. says:

    I have been working in the trade for 37 years. I have seen the transition from mechanical to electronic controls. My experience in automotive repair is more of a hobby. I believe the growing pains we are seeing in the HVAC industry is similar to what happened in automotive starting back in the late ’70s and early ’80s. Every one of those boards has one or more Integrated Circuits. Some are utilized as an EPROM, They are loaded with firmware that has a set of instructions that tells it what to do. One of the worst things to cause an electronic board to throw erroneous faults is low voltage. It scrambles the memory. Most memory today is non-volatile, so recycling the power will fix that problem. York doesn’t make the Integrated Circuits or EPROMS. This is an industry wide problem ranging from PC’s, to automotive, or any electronic device. I remember a time when technicians didn’t trust digital meters. The transition was resisted. Now techs don’t want to use analog. As technicians we will continue to be challenged. This is an excellent article and caused me to dig out my old analog, put new batteries in it and see it still works. Thanks for sharing!

    • Thank you for sharing your experience with everyone.
      The reason I started this blog was to share experiences and try to help others.
      Thanks again.

    • rjp says:

      I agree to a point about hvac electronics being less reliable than automotive. But I think one problem with hvac is their electronic packaging and cable terminations. How long would your Toyota or Ford run if the engine computer logic chips were exposed to the elements and critical wiring to those boards relied on exposed crimp spade lugs? Seal the modules and waterproof the connectors, add standard diagnostic ports across hvac brands and you would get 10-15 years out of the controls just like automotive applications. Go further and add detailed operating information at the thermostat, like delta t, subcooling and motor status, and you would have an hvac product ready to dethrone the Mitsubishi and Tranes of the world. Much like Apple did to IBM with consumer PCs and later Motorola and Nokia with cell phones.

      • Even though I have now been retired over 2 years, I still try to keep up with current technology. York has introduced a diagnostic module for the latest version of the control board which will provide time,temp, pressure, etc. They also have a USB port on the board and unit WiFI MODULE that can be left in the unit (or the contractor can plug it in at the site), tied into multiple units, and the contractor can stay in his truck and pull up all the operating data before ever going up on the roof. The board also has a LED display and programming buttons for configuring the unit.
        This has become the “standard” control for York RTU’S.
        Since York became part of Johnson Controls, there have been a lot of new innovations.
        I do appreciate your comments and agree with some parts but I do know that this industry is constantly changing for the better!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s