A/C Freeze Sensor - How do I check a faulty sensor?

[jmf27614]

Our Dometic Penguin II low profile AC/Heat Pump has an intermittent problem. The AC compressor turns off after 2 minutes (almost to the second). The freeze sensor is plugged in and lodged into the coils firmly. This happens both in cooler weather and hot weather. The fan stays on and the compressor stays off until we turn it off and back on.

We suspect that the freeze sensor is faulty. How do we check this? The heat pump works fine. This is a new MH and the AC is clean.

[jmf27614]

Doug, We don't have the 10 button control system, we have the Firefly multiplexer touch screen. The compressor works for exactly 2 minutes after starting and shuts down, but the fan stays on until the a/c is turned off on the screen. There is a delay of around 2.5 minutes to restart the compressor if you turn it off and on again immediately. The compressor always starts but intermittently turns off after 2 minutes if the sensor is installed, but always turns off if the sensor is not installed.

[dougrainer]

For the 10 button control system, they may have changed the design of the Freeze Thermister. IF there is NO OHM feedback, the system may shut down the compressor(when you remove from the coil) it does not have the normal OHM feedback. It sees a lack of the correct resistance(bad freeze Thermister) and shuts the Compressor down. If you do not want to take back to the dealer. Now, since you have the Firefly system, I assume you do NOT have the 10 button Dometic wall Tstat? I do not know if Firefly reads out the error codes like the Dometic wall tstsat. What happens if the sensor is installed and the compressor locks out after 2 minutes? If you wait 10 or 15 minutes, does the compressor come back on and then lock out again? If so, your compressor overload may be kicking out(bad compressor) Doug

E5 Open circuit or out-of-range Freeze Sensor. Air conditioner operation will be
locked out. Heat pump, furnace, heat strip, and fan operation can continue to
operate but displays the last temperature set-point.

[jmf27614]

The compressor shut off after a few hours this time. Restarted the A/C several times, ran the fan on high, turned the thermostat down - couldn't get it to run more than 2 minutes. Disconnected the freeze sensor, same result. So, I ran the heat pump for about 2 minutes. It did not stop when it reached the set temperature, so I bumped it down more and I finally had to shut it off. After that, the A/C worked fine. I don't see any freezing going on - but there does seem to be a thermostat issue of sorts. I'll probably call Thor and Dometic tomorrow to see whether they can shed light on this.

[Flute_Man]

Running your Fan on high speed may prevent it from freezing up in the first place. Give it a try and see what happens. You may call me if you wish.

[time2roll]

If the compressor never comes back on until you reset the thermostat... I am thinking it is a faulty thermostat. No idea how to verify. Possibly just unplug the freeze sensor and note any changes.

[jmf27614]

We only have one a/c. We have checked the separation gasket and sealed between the intake and exhaust. If we remove the Thermister from the coil, the compressor starts and shuts off after exactly 2 minutes. We can try disconnecting the plug from the board and see what happens. Once the a/c runs for longer than 2 minutes, most of the time it's good until we shut it down.

[dougrainer]

You go to the control board on the AC unit. You will follow the Freeze Thermister 2 wires to the control board. I have forgotten but you either jump the 2 wires and this bypasses the Thermister or you unplug the Thermister from the board and that bypasses. Either way, once you do it, the compressor should come ON. If the compressor does not come ON, then do it the other way. If you have 2 top units, just swap the Thermisters. Another way is to remove the Thermister from the coil, so it cannot sense any cool at all. If the Compressor runs and does not shut off, then the Thermister is bad. Another cause of your problem is the separation gasket between the Intake and exhaust of the cold air is missing and the unit is pulling COLD air back thru the evaporator. Doug