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I appreciate all of the comments on this issue. I still haven't revisited the particular unit in question, but hope to next week. In the meantime I'll be looking closely at getting a decade box.

Originally Posted by Sp4wN26

I am unfamiliar with this measurement tool, can you explain what it does exactly as you troubleshoot??

thanks

When working with a Trane unit that has the capability of a manual test such as on a Microtel or Reliatel board it will put you in the exact mode of operation which you want to test.

As an example when testing a unit with a two stage heat and a VFD, the "STEP' method does not allow enough time for the VFD to ramp up so you must leave it in this step mode long enough for the control to react. It also take about one minute for the combustion blower to switch from high speed and then to low fan speed. And this is a must check step as these units have inherent concerns. However when a problem exist such as a open limit or pressure switch there will be times when the control will skip that mode. Many times you will have to cycle the test over and over again and carefully follow the steps.

It is also necessary to go through the unnecessary steps which are working correctly. A decade box will within a few seconds put you in the exact mode based on the variable resistance method. It will remain in this mode until either you reset the power or the elapsed time has passed. This will eliminate any guess work whatsoever. That's it...leaving you to concentrate on the problem.

Also you can immediately cycle stages on and off from heat to cool or any mode you wish. No waiting at all...just go to work.

Now if you got 20 units to PM good luck waiting for the step method.

But that not just it. You can test the economizer function or the ECA module when experiencing problems by giving it a false OSA reading by using the correct temperature/resistance value to demand the unit to economize.

There are many more reasons but you get the idea.

As for a chiller I have had good results trouble shooting temperature input on the clear language display to simulate temperature.
This is also invaluable when testing an EXV and demanding it to position, but that's not for the faint of heart and I am sure I will here some slack on this. But I am not the one changing them out when problems come up either.

I can go on and on but now we are off the topic.

Originally Posted by alcomech

I have had good success with an IET RS-200 Decade box.

If anyone is going to work on this type of equipment an trouble shoot a Microtel or Reliatel board than this is the best way to accurately know the mode which you are in.

I am unfamiliar with this measurement tool, can you explain what it does exactly as you troubleshoot??

thanks

Originally Posted by fitzyfitta

Which decade box do you guys use and recommend?

I have had good success with an IET RS-200 Decade box.

If anyone is going to work on this type of equipment an trouble shoot a Microtel or Reliatel board than this is the best way to accurately know the mode which you are in.

Sure everyone knows how do perform a "Step" test, but it just not good enough for in depth trouble shooting.
Any one who has worked on these units when an erratic condition exist will tell you it can be time consuming.

Some get lucky for the most part, but when the components have failed or the performance has degraded such as an outside air sensor or mixed air sensor than their can be a lot of wasted time trying to understand the symptoms.

Its one of the correct methods of trouble shooting as recommended by the manufacture. Besides that there are many other and more important uses. If working on chillers or any other type of control work, this is a MUST have tool.

I understand those who don't have one have no other choice but to "Step" into problems, but there is a better way.



But I am still learning and looking for a new mentor.
_______________________
In a strict sense troubleshooting is not part of the repair..........understand the symptoms and you will find a solution.

Originally Posted by fitzyfitta

Which decade box do you guys use and recommend?

i built my own using products from digkey...i cost me about $75 which is pretty expensive for a regular ol' box but i made it really nice. it has a ball bearing selector switch, is water proof and can survive a drop off a roof.

sounds like the plug is removed. check the board, the led will blink when your in test mode

Sometimes you don't have good contact between the test screws. I usually use a pocket screwdriver and put it between the terminals on the back of the terminal strip. I use the step method, short between the test terminals one step at a time. If the unit is on a Trane Tracer system, the heat or cooling could be disabled on the front end. If it is, the test mode won't bring it on.

Which decade box do you guys use and recommend?

With jumper left in place unit will change steps every 30 seconds. For those without patience (like myself) take the jumper off for a five count then back on for five to get to the step you want. Will not go to a step with a safety open (limit/switch). Should also see the RTRM or UPC light flashing which indicates unit is in test mode.

Originally Posted by tech56

correct me if i am wrong but if i remember correctly, to use test mode without resistors, you need to jumper the terminals for one second and then remove jumper. to move to next test function jump T1 & T2 again for one second so on and so forth. hope this helps!

Absolutely right! test mode on trane RTU goes from fan to econo, compr1, compr2, heating etc.

It was also my understanding as I read that you said you jump tb1 and tb2 and sit back instead of jumping them for only a second or two!!

Yes I know that but the way the OP was written it sounded like he put the jumper between t1&t2 and left it in place. Maybe I read it wrong.

Originally Posted by alcomech

...nothing beats a decade box.

absolutely!

test mode only works if there isn't a problem mechanically. perhaps you have an open low pressure switch or other safety.

Originally Posted by tech56

correct me if i am wrong but if i remember correctly, to use test mode without resistors, you need to jumper the terminals for one second and then remove jumper. to move to next test function jump T1 & T2 again for one second so on and so forth. hope this helps!

As the OP has stated he has ran this unit in test mode for 15 minutes and has clearly lost his position. In this case there is no other or better method than to use a decade box. But if he does not have one than he can simply purchase a resistor as stated in the troubleshooting manual and test the mode which is of concern.

Otherwise he will need to be certain that he has tapped the terminals and follow the sequence so that he will be in the correct mode. Even for a very experienced tech and when experiencing erratic behavior it is difficult to follow the modes......nothing beats a decade box.

Originally Posted by HVAC_Austin

Sorry, I don't have the model and serial on me. But I will check to see that it's plugged into the board. I only recently began doing PMs on my own, so I'm fairly new at this. Why would the plug be disconnected?

There are times when some feel that it is easier to test directly from the board. I disagree with that method.

correct me if i am wrong but if i remember correctly, to use test mode without resistors, you need to jumper the terminals for one second and then remove jumper. to move to next test function jump T1 & T2 again for one second so on and so forth. hope this helps!

f its not reliatel it is not ltb1 & 2 it is test 1&2 two different sets of terminals on low voltage terminal board

Originally Posted by alcomech

What is the Model No. and Serial No.

Sorry, I don't have the model and serial on me. But I will check to see that it's plugged into the board. I only recently began doing PMs on my own, so I'm fairly new at this. Why would the plug be disconnected?

There are two type of boards. Microtel or the new Reliatel board.
If you are trying to test from the LTB test 1 & 2, you will need to verify that the wire plug is connected to the board.

You really should be using a decade box for variable resistance testing.

What is the Model No. and Serial No.

Originally Posted by alcomech

Is this a Microtel control board

To tell you the truth, I don't remember. I looked at so many of these things today my head is still spinning. What would it mean if it were a Microtel?

Is this a Microtel control board