HVAC Q-Logic Control System

[ColRon]

I've been experiencing a temperature display issue with my boat's AC system. It has a Cruisair Q3 display/control with the Cruisair Q-logic Control retrofit system connected to a Marine Air Systems VR12K-H AC/reverse heater. The boat has two systems and this one is located within the forward stateroom.

My issue is this, when the HVAC unit is turned off at the display the temperature displayed is the correct temp inside the forward stateroom. This has been verified with an independent room thermometer. As soon as I turn the unit on, the displayed temp begins to climb until its 7-10 degrees above the actual temperature. This tell me that sensor itself is reading correctly when the unit is off. Other than that and a small heat issue, the system works fine

I have completed the following troubleshooting of the problem, none of which have identified or corrected the issue.
1. Recalibrated the temperature setting.
2. Reset system to factory defaults.
3. Swapped the Q3 display/controller in the state room with the Q3 Display/controller in the Salon.

I am beginning to think the that the issue may reside with the Q-logic Control/Power board, but at almost $300 a pop, I don't want to just start switching boards to find that that might not be the issue.

One additional note, I typically kick on the heat cycle one per month as recommended. Currently, the system will not produce heat. I initially thought that this might just be a stuck reversing valve, but after tapping on it, I still could not get it to reverse. It just dawned on me that both the heat issue and temperature issue occurred around the same time frame and might be related.

Has anyone experienced similar issues? Any thoughts?

Thanks, Ron

[tomschauer]

Looks like that unit does not sense temperature at the controller. Seems it uses a remote sensor connected to the main board. Try to find the location of this sensor. Its most likely being influenced by something when the unit runs. It could also be that it has a loop water outlet sensor and the two sensors are connected in reverse so to speak on the control board.

Let us know what you find.

[ColRon]

Source of the post Looks like that unit does not sense temperature at the controller. Seems it uses a remote sensor connected to the main board. Try to find the location of this sensor. Its most likely being influenced by something when the unit runs. It could also be that it has a loop water outlet sensor and the two sensors are connected in reverse so to speak on the control board.

Let us know what you find.

Tomschauer, you are correct. There is only one temperature sensor and it is a remote sensor. The temp sensor itself is located at the return air filter at the HVAC unit. The sensor is connected directly to the controller/power board via a telephone type cable and RJ-45 type connector, from the Controller/Power board the signal is connected via separate cable and RJ-45 type connectors to the Q3 display/control. There is no water temp sensor attached. It is an option, but it was not installed.

The filter has been replaced to ensure that there was not a restriction in air flow. The sensor itself was also tested by moving it away from the HVAC unit, but the issue remained even after moving it away. It has a long cable so I was able to move it approximately three feet away from the HVAC unit itself. This is why I think it might be within the Controller/power board itself.

This issue just arose all of a sudden, was working properly one day and then later that same day we noticed the change in the temp displayed as it was abnormally high, but no change was felt in the temperature.

I have went through the Q3 manual for troubleshooting. It does state as a final option for "Erratic Temp" to replace the control/power board. All the other options were completed but no change was effected. But I'm not sure that I would define my condition as erratic. After its adjusts itself to 7-10 above the current true temperature when the unit is turned on, it works as you would expect, slowly dropping as the temp drops, just 7-10 degrees above the true temp.

Thanks, Ron

[bud37]

How old is your system.....if the troubleshoot flow chart leads you to a bad board, maybe a call to their tech department, if they have one, may help.......I am thinking if they had a run of funky boards , maybe there may be some help for you.
Re the heat....is your ambient too low now to get the heat to operate? ....good luck man...

[ColRon]

Source of the post How old is your system.....if the troubleshoot flow chart leads you to a bad board, maybe a call to their tech department, if they have one, may help.......I am thinking if they had a run of funky boards , maybe there may be some help for you.
Re the heat....is your ambient too low now to get the heat to operate? ....good luck man...

If memory serves me correct, it was retrofitted in 2014. I'll have to go find the receipt to be sure, but not that long ago in the grand scheme of things. Heck, I'm beginning to think that the HVAC unit itself is original because I can't find any info online for the VR models. The AC system in the Salon was replaced and the control system for the HVAC in the stateroom was retrofitted to match the one in the salon. As you may know Cruisair and Marine Air Systems are both owned by Dometic now and finding any official info online is sparse.

As far as the heating goes, currently the water temp is around 47 degrees and the air temp is 15 locally, I won't be able to test it for a month or so. In early March, I'm having her pulled out on to the hard to have the bottom paint redone and have a couple of other small things addressed that can only be done in the dry. So I have time to work out a solution. I am suspicious that the heat and temp may be related as both occurred around the same time. The heat was first, so I'm thinking it may not be getting signal from the board to the reversing valve, since tapping on it had no effect. I just don't know what voltage/ohm/etc. to test for.