Heat & A/C on at the same time!

[TheBeans]

My SIL just bought a used 5th wheel. When she recently went to turn on the heat she noticed immediately that the heat AND the a/c came on together and they were both blowing from the vents in the roof....no heat coming out of anything near the floor!

What would cause something like this to happen and has it happened to anyone else? Where should she begin to look to figure out what is going on here?

[Mont_G_J]

down home wrote:
Find a good the to sort out the thermostat/controls. Our has two furnaces and two heat pumps. It is cold with the heat pumps selected , the furnaces still come on first to bring the coach up to warmth fast, then shuts off and the heat pumps take over. Our Holiday Rambler Fifth Wheel operated the same way, I believe. And when it gets so cold the heat pumps aren't able to keep up the furnaces kick back in and heat pumps go off. No way a heat pump can blow both hot and cold at the same time, unless it also has heat strip and it is wired cockamamie, with it wired on the wrong side of the thermostat/switches. Heat pumps work in both direction reversing the ac cycle on heat to extract the heat from the air outside and heat the air inside but can only work in one direction at a time.

The OP said it was a new trailer to SIL and was getting heat and AC at the same time out of the overhead ducts. It seems to me the AC is running in the HP mode and the new owner doesn't understand that the air conditioner is capable of producing heat or cold depending on the mode.

[down_home]

Find a good the to sort out the thermostat/controls. Our has two furnaces and two heat pumps. It is cold with the heat pumps selected , the furnaces still come on first to bring the coach up to warmth fast, then shuts off and the heat pumps take over. Our Holiday Rambler Fifth Wheel operated the same way, I believe. And when it gets so cold the heat pumps aren't able to keep up the furnaces kick back in and heat pumps go off. No way a heat pump can blow both hot and cold at the same time, unless it also has heat strip and it is wired cockamamie, with it wired on the wrong side of the thermostat/switches. Heat pumps work in both direction reversing the ac cycle on heat to extract the heat from the air outside and heat the air inside but can only work in one direction at a time.

[Mont_G_J]

dougrainer wrote:

Mont G&J wrote:

dougrainer wrote:

Mont G&J wrote:
Perhaps it's like mine. My T-sat has a selection for 'Furnace' and in that case the furnace will come on and blow out of the lower furnace ducts. Also, I can select 'Auto' and in that case if the T-stat calls for heat the AC comes on and works as a heat pump blowing warm air out the upper AC ducts. If the trailer is warmer than the set temperature the AC blows cold air out of the same upper duct.

Sorry, not correct. AUTO does NOT turn on the Heat Pump function if you have a AC/HP upper unit. ALL AUTO does is allow the system to select the fan speeds and shut the fan OFF when temp is met. You still have to select HEAT PUMP on the wall tstat for the HP to function if you have one. If you do not have a HP display on your tstat, you do not have a HP. Doug

Doug, My AC does operate as a Heat Pump or Air Conditioner. In the 'Auto' Mode it will turn-on either function.
Below is copy and paste from owners manual.
G. “AUTO” - Auto Change Over Mode In the AUTO mode the system will automatically change the mode of operation from cool to heat or from heat to cool. In order for this mode to operate, the zone being programmed must contain either a heat pump, heat strip or furnace heating source. When in the AUTO mode, all pre-programmed operations for the heat pump, heat strip, and furnace will apply.

NOTICE it states the MODE MUST be programmed for that to happen. I will bet you have a CCC2 Dometic wall tstat. On your tstat, IF NO OPERATIONS PRE PROGRAMMED, then the system will NOT auto switch between AC and HP. So, if NO programmable Tstat(very RARE to have one), then the AC/HP will NOT switch between the 2. Doug

I'm not sure why you contiue to insist you know what I have and think I don't know. Please watch the video. Dometric Thermostat in 'Auto Mode'

[dougrainer]

Mont G&J wrote:

dougrainer wrote:

Mont G&J wrote:
Perhaps it's like mine. My T-sat has a selection for 'Furnace' and in that case the furnace will come on and blow out of the lower furnace ducts. Also, I can select 'Auto' and in that case if the T-stat calls for heat the AC comes on and works as a heat pump blowing warm air out the upper AC ducts. If the trailer is warmer than the set temperature the AC blows cold air out of the same upper duct.

Sorry, not correct. AUTO does NOT turn on the Heat Pump function if you have a AC/HP upper unit. ALL AUTO does is allow the system to select the fan speeds and shut the fan OFF when temp is met. You still have to select HEAT PUMP on the wall tstat for the HP to function if you have one. If you do not have a HP display on your tstat, you do not have a HP. Doug

Doug, My AC does operate as a Heat Pump or Air Conditioner. In the 'Auto' Mode it will turn-on either function.
Below is copy and paste from owners manual.
G. “AUTO” - Auto Change Over Mode In the AUTO mode the system will automatically change the mode of operation from cool to heat or from heat to cool. In order for this mode to operate, the zone being programmed must contain either a heat pump, heat strip or furnace heating source. When in the AUTO mode, all pre-programmed operations for the heat pump, heat strip, and furnace will apply.

NOTICE it states the MODE MUST be programmed for that to happen. I will bet you have a CCC2 Dometic wall tstat. On your tstat, IF NO OPERATIONS PRE PROGRAMMED, then the system will NOT auto switch between AC and HP. So, if NO programmable Tstat(very RARE to have one), then the AC/HP will NOT switch between the 2. Doug

[Mont_G_J]

dougrainer wrote:

Mont G&J wrote:
Perhaps it's like mine. My T-sat has a selection for 'Furnace' and in that case the furnace will come on and blow out of the lower furnace ducts. Also, I can select 'Auto' and in that case if the T-stat calls for heat the AC comes on and works as a heat pump blowing warm air out the upper AC ducts. If the trailer is warmer than the set temperature the AC blows cold air out of the same upper duct.

Sorry, not correct. AUTO does NOT turn on the Heat Pump function if you have a AC/HP upper unit. ALL AUTO does is allow the system to select the fan speeds and shut the fan OFF when temp is met. You still have to select HEAT PUMP on the wall tstat for the HP to function if you have one. If you do not have a HP display on your tstat, you do not have a HP. Doug

Doug, My AC does operate as a Heat Pump or Air Conditioner. In the 'Auto' Mode it will turn-on either function.
Below is copy and paste from owners manual.
G. “AUTO” - Auto Change Over Mode In the AUTO mode the system will automatically change the mode of operation from cool to heat or from heat to cool. In order for this mode to operate, the zone being programmed must contain either a heat pump, heat strip or furnace heating source. When in the AUTO mode, all pre-programmed operations for the heat pump, heat strip, and furnace will apply.

[dougrainer]

Mont G&J wrote:
Perhaps it's like mine. My T-sat has a selection for 'Furnace' and in that case the furnace will come on and blow out of the lower furnace ducts. Also, I can select 'Auto' and in that case if the T-stat calls for heat the AC comes on and works as a heat pump blowing warm air out the upper AC ducts. If the trailer is warmer than the set temperature the AC blows cold air out of the same upper duct.

Sorry, not correct. AUTO does NOT turn on the Heat Pump function if you have a AC/HP upper unit. ALL AUTO does is allow the system to select the fan speeds and shut the fan OFF when temp is met. You still have to select HEAT PUMP on the wall tstat for the HP to function if you have one. If you do not have a HP display on your tstat, you do not have a HP. Doug

[time2roll]

Do you have propane? Is the propane turned on? Any chance you have a heat strip or heat pump A/C unit?

[Fulltimers]

Sounds like you have a heat strip inside the AC unit. Some AC units will do cold or hot.

[Mont_G_J]

Perhaps it's like mine. My T-sat has a selection for 'Furnace' and in that case the furnace will come on and blow out of the lower furnace ducts. Also, I can select 'Auto' and in that case if the T-stat calls for heat the AC comes on and works as a heat pump blowing warm air out the upper AC ducts. If the trailer is warmer than the set temperature the AC blows cold air out of the same upper duct.

[dougrainer]

1. Need Brand and Year Model of RV and Brand Model of AC and type wall tstat. Without this info nobody can help you.
2. ODDS are she is NOT activating the Heat(furnace) at all. She is activating the Roof AC system and is seeing the air blowing out the roof vents.
3. Depending on the Brand and Model AC and tstat, Dometic's on some units, if you DO NOT have the roof AC Fan set to AUTO, the Roof AC fan will come ON when you activate the floor LP furnace. That is normal on this type system. But the furnace should still come on and blow out the Floor vents. Doug

[jdc1]

How can you both heat and cold from the same vent? LOL. See the above last line/

[way2roll]

My new FW will allow me to set the heat and AC at the same time. The theory is that if you were to be away all day and it's cold in the am but hot in the afternoon, the heat can run to bring it to temp X and the AC to temp Y. If the temps were set to be the same, I guess it's possible they could both come on at the same time since they are independent systems. They don't use the same ducts however.

I guess questions would be how did she know both were on ? Was there a panel that told her this? And how did she know they both came out of the same duct? Does she have a heat pump in her AC unit?

It is possible that the ducts could have held hot air when the AC turned on and felt warm until the ducts cooled?