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The red light indicates it's either heating or in defrost mode
Check the outdoor unit if the compressor is running - the large pipe on the outdoor unit should be hot on heating or cool to touch on cooling
When in heating mode - the indoor fan will not start until the indoor coil is warm enough
If the reversing valve that changes from heating to cooling is faulty then you may encounter the same symptoms too
Probably need a Refrig Tech to have a look at it?
If the compressor is off and the heat coil is on - this is normal for the "E" or emergency heat setting. Check for proper connections between the Heat-pump, furnace(heat source) and the thermostat and that the thermostat is capable of controlling a heat-pump with secondary/emergency heat units. Thermostats designed for this have 4 settings: Cool / off / heat / E(emergency heat). in the "heat" setting, both the Heat-pump and Aux heat work together to maintain temperature. In the "E" setting, only the Aux heat source is used. The "E" setting should only be used in extreme cold - when the Heat-pump can no longer produce heat.
Sound like the change-over valve on the heatpump is not switching. Could be the valve is stuck, or bad. Or the thermostat is bad and will not send voltage, or is sending voltage to your change-over valve.
(Some systems energize the CO valve to cool, while others de-energize the valve).
Usually the color coding for the thermostat wires on a heatpump are orange and yellow. The yellow wire usually energizes the compressor contactor, and the orange wire energizes the changeover valve. Now depending on what your system does in terms of energizing or not energizing the CO valve to invoke heating or cooling mode is not known. You can try jumping across the thermostat to see if the CO valve is working. Or you can even try placing the stat in heating mode and see if you hear that loud "Woosh" when you switch between heating and cooling modes at the stat.
What often happens is the cylinder inside the CO valve gets stuck, especially if the system has sat off for an extended time. By workign the stat from heating to cooling (reversing the porting on the CO valve) will cause the valve to free itself up.
If you cannot hear that woosh as the changeover valve switches between heat and cooling, it is possible the CO valve is bad, or there is an issue in the electrical or control side of your system. Such as a bad base or switching circuit in your stat, or control issues other places.
The problem is in the thermostat wiring. Y1 on an air conditioner, brings on the cooling. On a heat pump, it brings on the compressor, which generally fails to heat mode. The O wire operates the reversing valve, which brings on cooling. If these wires are reversed, or not hooked up, you will not get cooling.
Unfortunately, your rear unit is calling for heat. If you put the rear unit on heat pump mode, does it then cool? The reversing valve is energized in the cool mode of these AC's. So there is no real way to bypass it. I would check the thermostat and the control board in the unit to make sure that the switches are set correctly.
In the service manual section of the dometic/Rooftop RV Air Conditioner section. I have posted service manuals for the Heat Pump and the Comfort Control.
Look for any refrigerant leaks - no or low refrigerant can cause problems in both modes. The unit may be going off on low suction.
The unit may be stuck in the heating mode.
Make sure the system is calling for the correct mode (cooling or heating) - some systems are auto, but if you can, select cooling since that is the requested mode. Check for power at the reversing valve inside the condensing unit. If power exists, then the reversing valve is stuck. It could also be the reversing valve solenoid coil, so make sure that isn't bad. There should be a strong magnetic field at the solenoid coil.
If you can hear the reversing valve clicking (moving), check the T-stat and make sure it will switch modes. Also check the reversing valve relay (those can be located in either the indoor unit or condensing unit).
On heat pumps, the normal setting is simply an air conditioner working in reverse. The EMT or AUX heat is a supplemental heating system using electric heating elements instead of the hermetic (compressor) system. As far as why the regular heat does not work it can be one of many things. low freon charge. reversing valve not functioning. The defrost cycle not working. Take your pick. you may want to call a service man to repair it as the electric (EMT) is not as efficient.