Viewstat ENV-VST-C not triggering Compressor

terrmul

Been getting a bit of a run around with an issue on the ENV-VST-C thermostat. We had this installed for several years without issue then it failed and we sent it in for repair. Since getting it back and using the following set up it won't heat yet I'm certain we haven't changed any wiring or settings. We sent it in for repair again assuming it was a thermostat problem but still have the same issue with a new one.

The set up is:
Single Stage Heat Pump
Electric

Connections are as follows:
RH/RC Power- Red
C Common - Brown
O Reversing valve - white
Y1 Compressor - yellow
G1 Fan - green

When the system calls for cooling the compressor, fan and reversing valve are all energized.
When we call for heat the fan is energized but NOT the compressor and so NO HEAT. (This happens whether or not Axlink is connected.)

We have jumpered W1 to Y1 which is a work around but is not the solution as there seems to be a gap between the fan turning on and the heat kicking in.

TurnipTruck

Where is your balance point set? If it's higher than the outdoor temperature, the compressor will not start. Instead, W1 will energize as a means of running the backup or aux heat.

Sent from my SAMSUNG-SGH-I317 using Tapatalk 2

terrmul

I suspect this may be the problem however I'm not on site. The balance point is most likely to be at the default setting. My question is where does the stat get the outdoor temp from? We've disabled the iWeather/forecast info? Maybe that is the problem?

Gonna check it out but wouldn't that mean that the compressor isn't energized when cooling too? Currently it energizes when cooling but not when heating.

TurnipTruck

You could only get the outdoor temp from a wired sensor with iWeather disabled. The stat is probably thinking that the outdoor temp is 32. I believe the default balance point is 40 which would mean your compressor would be locked out. Balance point has no effect on cooling operation. Balance point is the temperature at which your heat pump would be running less efficiently than your backup heat source.

terrmul

So the balance point was set to 30deg, the outside temp was 32deg, in theory it shouldn't have affected the compressor however I lowered the balance point to 20 and that seems to have done the trick. Thanks for your input.

terrmul

So I just got a call from the client - no heat. I told him to set the heat point to 1º above room temp and the heat kicked on. If set higher than a degree or two though there's no heat. Am I missing something or is this a firmware issue?

TurnipTruck

Is there a backup heat source for the heat pump? In most systems there are electric coils or maybe a propane furnace that serves as backup. If there is, it should turn on if your room temperature is below the heating setpoint by greater than the first stage differential setting.

terrmul

No there is only one heat source, no backup. Should we just set the first stage differential to the max setting?

TurnipTruck

First of all, my answers to your questions are not to be taken as any official guidance. That being said, my instinct would be as follows:

Keep your mode setting as single stage heat pump.

Connect your compressor to W1 and Y1.

Connect your changeover valve to O or B as necessary. The changeover valve is what causes your system to change from a heater to a cooler. Most systems use O to changeover to cool. Some use B to changeover to heat.

The balance point and first stage differential settings would become irrelevant. You will still see the AUX on the screen though when your non-existent backup would have been running.

There is a hotfix firmware available that I would recommend if you plan on using the program mode for setpoint scheduling. It's version 3.12.

TurnipTruck

To this I would add that the more appropriate setting for the thermostat mode would be "Boiler with A/C" as that is the only setting for a truly single stage heat (which is what you have with no backup system). However, the interface to the heat pump would require external relays.

terrmul

Thanks for your input. Much appreciated. We have tried shorting W1 and Y1 but that seemed to still leave a gap between fan on and heat on. Will test again and see what we get!

TurnipTruck

I have the stats installed in my own house. I notice a several second delay between fan and heat and activation. That shouldn't be of concern. I would LOVE to see a 60 second delay of fan off after heat/cool off, but I couldn't talk the powers that be into it. That's another story.

What firmware is on the device? You can see it in Studio or on the Axlink channel setting page.

terrmul

It's v3.01/3.04. I guess I should add that hotfix....