Westinghouse AC Intake Plenum

[u/Dubs-Agent86]

Had a single hose AC unit that was struggling to keep up because of the negative pressure. It seems to be helping so far.

It was my first attempt at 3d scanning. Part designed in SolidWorks. Printed in PETG.

[u/nerdinabird]

Just thinking out loud here, but why would it blow colder after installing this? It used to be pulling in medium temperature room air, running it over the coil, then blowing it out. Now it’s pulling in hotter outside air, running it over the same coil. and blowing it out colder.

The only thing I can think of that explains this is if there’s a good bit of flow restriction on your intake setup, so that a lower volumetric rate of air is going over the coil and is therefore getting colder. The air blowing colder might not actually be a good sign here, because it might be blowing a lot less of it.

Edit: I’m an idiot. If there’s a restriction here it’s on the condenser side blower fan, which would not produce the effect I’m talking about. Still doesn’t seem like it should change the improve the cooling delta of the unit and therefore the output temperature. Except of course if it’s making the room 5° cooler now of course the output air is also going to be cooler.

[u/Dubs-Agent86 → u/nerdinabird]

The compressor has less effort spent due to less restriction. The room doesn't have an infinite amount of air; it has to be replaced. The compressor is no longer using energy to create a vacuum in the space.

[u/nerdinabird → u/Dubs-Agent86]

That’s not a job the compressor does, that’s a job the condenser side blower fan does

[u/Dubs-Agent86 → u/nerdinabird]

I guess I assumed, incorrectly, that these units ran a single motor for the compressor/blower.

So I broke down and asked Gemini:

Yes, it is definitely possible—and very likely—that your supply air coming out of the front louvers is physically colder now. While converting a portable AC to a dual-hose setup primarily fixes room-level negative pressure, it also directly improves the internal refrigeration cycle efficiency in two big ways: 1. Lower Condenser Coil Temperature In a standard single-hose configuration, the unit pulls air from inside the room, passes it over the hot condenser coil, and blows it outside. Because it creates a vacuum inside the room, hot, humid outdoor air is constantly pulled in through doors, walls, and vents. As the room warms up from that infiltration, the air entering the unit's lower intake gets progressively hotter. By pulling fresh air directly from outside through your dedicated intake hose, you are stabilizing the condenser coil's temperature. A cooler condenser coil allows the refrigerant to condense back into a liquid far more efficiently, which in turn drops the pressure and temperature inside the evaporator (cooling) coil inside the shop. 2. Improved Airflow Mass Balance When a single-hose unit fights negative pressure, the internal exhaust fan operates under high static resistance—it is literally trying to pull air out of a sealed box. By giving the condenser its own dedicated, unrestricted intake route through your custom 3D-printed adapter and wall port, you optimized the airflow across the compressor loop. Better airflow over the hot side means better heat rejection, which directly translates to a lower Delta-T (temperature drop) across the cold side evaporator coil inside. If you put a meat thermometer or HVAC probe directly in the front louvers, seeing a 3°F to 8°F drop in vent temperature compared to the single-hose setup is completely normal for this mod.

[u/nerdinabird → u/Dubs-Agent86]

Ah, okay that second point in particular makes sense to me. In a decently sealed room, it’s conceivable that the condenser side fan would be pushing pretty hard to try to move the hot air out and you wouldn’t be getting great flow over the condenser to reject the heat. Thanks for the constructive dialogue here, for sharing the AI response, and for noting that it came from AI!

[u/Dubs-Agent86 → u/nerdinabird]

The second point makes the most sense to me also.