MHI Standard Wired Controller

[back2space]

Guys

Just had a call in tonight where the site were complaining of being too hot. The controller is locked through the internal functions where the site can only adjust set point and fan speeds and not the operating mode (heat/cool) it is left in Auto mode... the triangle.

There is an option in the controller to be able to stop the user changing the operation mode on the controller. However we assumed that if we left it on automode that when the user altered setpoint that the system would changeover if needed.

Max set point is 24C and min is 22c however the room is never entering cooling mode.

Having checked that the outdoor is running when it is set to 22C the outdoor isnt running and only seems to be running on heating mode.

However if we enable the mode changeover function in the controller and switch it onto cooling manually, the system works fine.

So our guess is this, if the system was set to the autochangeover (triangle mode) and was calling for heating then when you disable the changeover function so that it is locked to the auto mode the system cannot even change over to cooling on the automode due to the function being disabled.

We always thought this would be possible in automode even if the changeover function was disabled as we thought this just stopped the user messing about with it.

Thought would share this with you.

[Brian_UK]

You could be right but with most of the auto-changeover controllers the normal switch points are expanded.

Whereas if in 'cooling' mode and a set point of 22°C the unit will switch on at say 23° and bring the temperature back to 22°.

When in 'auto' mode the temperature range may be expanded by 1.5 to 2° so, having been in the heating cycle the unit will need to sense a temperature of 22 +1° + 2° (25° ish)before it will change from heating to cooling mode.

Don't take these figures as gospel but it helps to explain the delay in switching from one mode to the other.

[back2space]

Yeh but what we find when its in auto mode without the lock on was that if you change the temp then turn the panel off and on it will then change into heating cooling straight away rather than waiting the 15minutes parameter.

The set point was 22 and the temp in the room was 25C so we do think this is how it sets.

I do understand your points of the paremeters involved with temps before it changes over this is to avoid it changing over all the time backwards and forwards.

[back2space]

We also are not sure what a particular option in the I/U FUNCTION menu of the controller means.

This comes up on the controller as

"FREEZE PREVENTION TEMP" & the options are "Hi or Lo"