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footdoc · 02-08-2007, 04:52 PM

On my rear unit when the stat is set to heat pump and the temp drops into the mid 30s, hydrohot comes on, as it should...Up front with the same situation, the heatpump fan quits and the compressor runs..never switching over to hydrohot. Been checked by local repair shop and dip switch settings confirmed on the phone with Dometic and Newmar conference call. As it rarely gets that cold here, they cannot activate the problem..only when I'm camping up Nawth in the woods...not a great place to get a tech to look at it. Any ideas what is wrong? I'm basically stuck with this situation if they cant cause it with our less than low temps here

footdoc · 02-08-2007, 04:52 PM

On my rear unit when the stat is set to heat pump and the temp drops into the mid 30s, hydrohot comes on, as it should...Up front with the same situation, the heatpump fan quits and the compressor runs..never switching over to hydrohot. Been checked by local repair shop and dip switch settings confirmed on the phone with Dometic and Newmar conference call. As it rarely gets that cold here, they cannot activate the problem..only when I'm camping up Nawth in the woods...not a great place to get a tech to look at it. Any ideas what is wrong? I'm basically stuck with this situation if they cant cause it with our less than low temps here

rebelsbeach · 02-08-2007, 11:02 PM

Joe-K · 02-09-2007, 03:33 AM

Larry,

Hmmmm...not being able to troubleshoot the heatpump because it's too warm

Man, I'm jealous being in Pennsylvania now at 4 degrees outside

Anyway, I can't help you with the actual diagnosis of the unit's switchover as I'm not familiar with it, but if the techs know the operation of the unit, they should be able to simulate the cold conditions to cause the switchover. Usually most designs have testing capability built into the design to allow cold operation troubleshooting.

The unit probably has a thermistor registering the outdoor air temperature. Thermistors can be either positive or negative meaning their resistance can either increase or decrease as temperature changes. If it's positive, resistance increases with temperature, if it is a negative thermistor, it's resistance decreases with an increase in temperature.

In the positive case, as the temperature drops, the resistance drops which can be simulated by putting a resistance in parallel with the thermistor. By electronically simulating the colder temperature by either adding resistance or removing resistance, they should be able to adjust the switchover point and troubleshoot the system.

The other option is to actually simulate cold conditions if the repair shop doesn't want to touch the electronics. Insist they contact Dometic and determine the location of the external temperature sensing device. Hand them a can of freeze spray and tell them to spray the device. Freeze spray is available at most electronic stores and is used for thermal troubleshooting. It will cool down well below 0 degrees F to allow for troubleshooting.