Mobile home ducting

[jb8103]

This mobile home has a Miller furnace inside and a Coleman AC package unit outside. Both units have their own blowers.

When the AC runs, the cooled conditioned air blows out of the furnace. It acts like another register.

What is the situation here?

[RegUS_PatOff]

I'm not a HVAC master, but normally, the AC "package" outside is the Compressor and it's cooling Fan.

The AC Evaporator (cold) Coil is mounted inside the Furnace Blower area and uses the Furnace Blower to circulate the cooled air.

[ACtechGUY]

How is the furnace duct connected to the cooling duct. Is it something like the furnace and package unit share the same supply duct and when the cooling fan is blowing , cool air exits from the furnace intake(where the filter is)?

If so you may have to rig a manual damper on the furnace outlet to stop air from going through the furnace.

[RegUS_PatOff]

does the AC "package" have it's own cooling ducts ?

model number ?

[jb8103]

I'm not a HVAC master, but normally, the AC "package" outside is the Compressor and it's cooling Fan.

The AC Evaporator (cold) Coil is mounted inside the Furnace Blower area and uses the Furnace Blower to circulate the cooled air.

That would be a split system with a line set running into the furnace closet to the evaporator. In the above case, both the evaporator and condenser are located outside in a single cabinet. Aside from the air return duct to the evaporator, both units use the same distribution ductwork throughout the home.

[jb8103]

How is the furnace duct connected to the cooling duct. Is it something like the furnace and package unit share the same supply duct and when the cooling fan is blowing , cool air exits from the furnace intake(where the filter is)?

That's what is happening. The furnace is a downflow installed directly over the trunk, while the AC feeds the trunk from the side. I've never done an installation on one of these and assumed that some kind of damping arrangement would be provided. I haven't had a chance to revisit the home since the summer, but it occurs to me now that if the AC can blow up through the furnace, the furnace can blow out through the AC, essentially heating the exterior cabinet, and there could be significant heat loss there. There might be a one-way damper rigged in the AC feeder to the trunk to prevent this, I didn't think to look at the time.

My mother's system is like this and I plan to get over there tomorrow and have a look.

I'm a newbie at this myself, having a community college certificate in HVAC but not much field experience.

What to look for?

[ACtechGUY]

You have the right idea. there has to be one or more dampers to prevent air from going where it should not be going . This may be a job for a duct pro. Especially if we are talking about metal duct. The situation gets easier if all you have is flex ductwork.

[Bobice]

I assume that the outside package unit is for A/C only therefore I would install a damper where it enters the supply plenum.

You could use a manual or thermostatically controlled electrically operated one.

I see you are finding out that there is nothing like hands on experience.

[jb8103]

I see you are finding out that there is nothing like hands on experience.

So true. The only sheet metal instruction we got was in basic shop fabrication, nothing about field work. Big difference.

Anyway, I didn't see any manual damper control on my Mom's setup, but there was no indication of heated air in the outside cabinet either. Everything was ambient: freezin' azz cold. Well, nothing is broke so further investigation can wait until spring.

[Bobice]

Quote: freezin' azz cold.

Sorry but there is no such thing as Cold.Rember Cold is the absence of Heat.

[jb8103]

Quote: freezin' azz cold.

Sorry but there is no such thing as Cold.Rember Cold is the absence of Heat.

According to my favorite scale it was 480 degrees out there, which is actually below freezin' azz cold.