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Isolate the communications to find the source of the problem

Did you try to disconnect the PT Link from the Wattmaster and let the unit operate stand alone? If you disconnect the communications to the Wattmaster and the problem goes away then you know it's a communications issue. You could also try disconnecting the BACnet MS/TP communication from the PT Link to see if it's BACnet commands from the network setting the values to zero. You need to try and isolate the problem. Good luck.
We had a job with a similar setup and the owner ended up ripping out all of the controls in the AAON units and hardwiring all of the controls to a controller. With the owner provided controls and the digital scroll compressor the discharge trend was a flat line.

Originally Posted by CountryBumpkin

Do these VCM's have expansion modules on them? I had a unit that had VCM's with the expansion modules and the cable that tied the expansion module to the VCM was loose and because the fan proving switch was tied to the expansion module the unit would shut down whenever the VCM lost comm with the expansion module. What does the date and time show when you look at the handheld? If it shows something like 99:99:99 then that means there is a problem with one of the wattmaster boards.

I installed new cables between the VCM, expansion board, and the modulating gas heat board. On this unit they are not using a fan proving switch as a input to the VCM or the expansion board. As far as the time goes. I will check into that tomorrow on my next visit. Thanks for the reply.

Originally Posted by klrogers

Best thing I ever done with a VCM was pull it out and replace with a controller that I can program myself. VCM would randomly change set points and not maintain close to set point, now runs 24/7 with 0.5°F of set point

Kevin

I will agree with you on that. I wish I could have done that on the 6 AAON units I recently installed.

Best thing I ever done with a VCM was pull it out and replace with a controller that I can program myself. VCM would randomly change set points and not maintain close to set point, now runs 24/7 with 0.5°F of set point

Kevin

Do these VCM's have expansion modules on them? I had a unit that had VCM's with the expansion modules and the cable that tied the expansion module to the VCM was loose and because the fan proving switch was tied to the expansion module the unit would shut down whenever the VCM lost comm with the expansion module. What does the date and time show when you look at the handheld? If it shows something like 99:99:99 then that means there is a problem with one of the wattmaster boards.

Originally Posted by lwarren

When you say "I can hook up to the wattmaster VCM controllers and multiple points are reading 0." I assume you are using the handheld service tool to do this? If so, then I don't think there is a problem with the BACnet side or PtLink.

I am hooking up with the hand held service tool after different points go to zero on the BACnet Trend. I was told by Wattmaster that the values I read from the hand held were the last values that the BACnet network wrote to the unit before I disconnected the cable and hooked in the service tool. Wattmaster claims bad data could be coming from the BACnet system and zeroing out a few of the points in the Wattmaster from time to time.

Is there some sort of software I can use to Trend the BACnet network and try to capture the problem? Also is there a software that can Trend the Wattmaster network while the BACnet signals are still coming in? Prism II?

I talked to a integrator at Wattmaster and they told me that the Wattmaster VCMs on these units may be bad. I guess the EEPROM is a SS1016 and the version is a 1.51. I guess this is one of there older boards. They claim they have a version 6.5 VCM out now. They are recommending upgrading the board due to all of these weird issues we are having. I just want to make sure that this is totally necessary. I am not sure how much money these boards run, but I do not want to replace them unless they are bad. Does anyone else have any ideas of what else I can check? Like I said various points are going to zero on the VCM controllers. It is the same few points on each of the units. It isn't a communication loss as most of the points are still readable at the time of the fault condition. The unit is seeing the SA go to zero and shutting down on freeze.

When you say "I can hook up to the wattmaster VCM controllers and multiple points are reading 0." I assume you are using the handheld service tool to do this? If so, then I don't think there is a problem with the BACnet side or PtLink.

Wattmaster VCM Controls Communicating over a PTLINK - Problem

I acquired a new job with a Automated Logic System using BACnet MS/TP to communicate over a PTlink to some Wattmaster VCM controllers. There are two controllers on the network. I guess ever since day one they have been having some issues. The RTUs will intermittently shut down due to the units seeing a 0 degree discharge air temperature. I have trended all of the different points out of the units on the BACnet side of things. I can see a few of the points go to 0 at the same time. The thing is the units are actually responding to this 0 and going off on freeze. So the fans shut down until the sensor shows valid again. I can hook up to the wattmaster VCM controllers and multiple points are reading 0. It does this on all of the controllers randomly throughout the day. I can I track down what is causing this problem. I don't know if it is some sort of network problem on the BACnet side of things and points are getting written to the units that shouldn't be. I have contacted wattmaster and they are thinking it may be there controllers, but I am not sure if that is true or not. What kind of things can I check to try to track down this issue?

Thanks