UndermountAC.com 12V & 24V Air Conditioning System

The Basics

What is it and why do I need it?

Our under mount air conditioner allows you to have comfort in your van or RV without hindering your roof space with a roof mount air conditioner. This satisfies the needs of stealth campers, campers with HOA rules not allowing RV's, or if you simply require the roof space for as much solar as possible. Our compressors are proven and robust variable speed units. The entire system is assembled from quality automotive grade components giving you a lasting long term product backed by a warranty and long term parts support if you ever needed. Our shelves are stocked if you ever need a part.

How efficient is it and what sort of power draw can I expect?

Our entire system is built around efficiency. We use larger surface areas on our condensers and evaporators to allow for maximum cooling for the power draw. Watt per BTU/h we are the best in the market. Our multi-speed compressor is utilizes two speeds controlled by your thermostat. If your application requires maximum cooling possible, a higher speed can be activated.  900Watts of input power will result in 12,000BTU/h or cooling. 1100Watts of input power will result in 16,000BTU/h of cooling. The compressor is a variable speed unit with easy start and will slowly start and ramp up to its desired speed. No power surge's or heavy draw's at startup.

How can I control it?

Our 12V systems now come standard with our cellular thermostat.

This thermostat is a touchscreen and button controlled thermostat. It is entirely your choice on how you choose to control it. In addition to the these two methods you may choose to control it remotely using LTE/Cellular. The first year of service in included and starts the moment you sign up for the app is you so choose.

The thermostat is a touchscreen smart thermostat and will allow you to limit fan speed, compressor speed and allow you to operate the fan in recirculate mode by itself. The thermostat will also allow you to tie into your custom in-floor heating if you choose to (Not compatible with Rixxen's thermostat) or use our new HVAC blower with built in heating coil.

Is the thermostat available in black? Not yet We are working on it, in the meantime the Krylon plastic paint adheres really well.

Can I install it myself?

Yes, absolutely. 90% of our customers are self installers. Our newest version of our kit (V3) is clearly marked and only requires 3 components to be mounted, power provided to the compressor and hoses to be made. Hoses are as easy as PEX home plumbing. Simply mark, cut with a utility knife, slide the fitting in place and crimp it with a PEX crimper. Once everything is mounted we recommend going to your favorite mechanic shop to have the system purged and filled with pure r134a refrigerant. You can view a full how to install video here: Tim's install video

What are the available mounting options?

Our newest standard condenser can be mounted horizontally or vertically. The better airflow you can give the condenser access to, the more efficient the overall system will be. The more cooler air running across the condenser the faster the system will be able to shed heat resulting in overall better system efficiency and use of power. Standard the condenser comes with 90 degree horizontal or vertical mount brackets. We are currently nearing completion of an angled mount for the Mercedes Sprinter VS30 144" wheelbase vans. This mount will utilize two factory holes in the frame on the passenger side in front of the rear tire. No ground clearance will be lost, and no drilling is required to utilize this mount. Availability will be mid February.  We are also developing a Ford transit mount that will angle the condenser allowing for better efficiency and quieter fan flow. 

How tough is this system? Can it handle all conditions?

Absolutely. Everything is sealed automotive grade. Our external components use proven components that are robust and up to the task of handling harsh climates. Our systems will stand up to River crossings, winter conditions or dust just like the rest of your van will. The same ratings are on all of our wiring harnesses and equipment as the factory systems of your van's engine bay. We ask that you take the same level of care as you would the rest of the van and give the condenser at least a yearly wash down. If you are washing the rest of your van after driving through dust or mud, you should also wash down the condenser and compressor.

How loud is it?

Our latest generation of condenser fans come with two options. Standard SPAL S-blade fans are 78dB in direct line of sight of the condenser 5' away. (Quieter when mounted under the van out of direct line of sight). Our Hush fan upgrade changes the fans out for a set of balances precision units that lower the overall output by 6dB (That is more than twice the noise output less) but more importantly changes to tone of the fans from a typical higher pitched fan/motor noise to only the sound of air movement. This hush kit is an industry first and exclusive to us! (Please note all dB ratings were tested at 13 system volts. Axial fans will increase in speed, therefore increase in their noise output as voltage goes up as the blade RPM increases)

What else will you need?

You will be required to provide the wiring necessary to run to the compressor circuit breaker, You will also be required to rent, purchase or borrow a Pex style Knipex tool to crimp the A/C line connections. Lastly you will be required to purge and fill the the system with R134A refrigerant. You may absolutely do this at home but we recommend heading to your local mechanic and having them fill using their automated machine. Please be sure they follow our instructions! 


Installation Manual for Version 3 Kits (Sold after February 1, 2023)

Download Here

Installation Manual for Version 2 Kits (Sold May 15, 2022-Feb 2023)

Download Here



Deeper Dive

What are the differences between your two evaporator options?

The evaporator on the left (Our ducted slim evaporator) is a US made evaporator with 4 2.5" ducts built in. The evaporator has a SPAL brushless blower exposed and attached to the back of it. This blower has open fan wheels and can intake air from anywhere around the unit allowing a much closer cabinet to be fitted. This is a heat/cool HVAC model meaning it has a built in water heat coil allowing you to use our system and your vans ducting for heat either from a Espar/Webasto hydronic heater or your van's engine. The evaporator has two condensation drain ports and the enclosure is entirely made in the US from ABS plastic.

The evaporator on the right (916 Proair model) is a steel encased US made evaporator. It is Cool Only and the preferred choice for high humidity environments as it has a larger evaporator core. This evaporator also features a SPAL brushless blower that is internal of the unit. If you require ducting, we offer 2.5" ducting adapters for this evaporator.

How heavy is it?

We understand that weight is always a factor in your build. Here are the individual weights for each component. Please add 2lbs of refrigerant to your total, along with about 4lbs of hose.

916 Evaporator 22lbs

HVAC Evaporator 14.8lbs

KC Condenser 23.7lbs

Compressor/Relay Board/Mount and wiring 26.1lbs

Why do we use brushless evaporator blowers? 

Quality. Brushless blowers are quieter than their brushed counterparts. Due to the nature of the way the brushless motor is balanced the entire assembly is much more precise and balanced resulting in a smoother quieter operation. No resistors means no unexpected losses. Standard 3-speed evaporator blowers rely on resistors to slow down the speed. This means the wattage required to power brushed blowers is the same regardless of what speed selected, the difference goes into a set of resistors that transfer that energy into heat. While more expensive, brushless blowers are 100% the way to go.

What sort of BTU output can I expect?

The unit was tested Testo 605i Thermohygrometer's utilizing all three of the available compressor speeds. Attached are the calculated outputs.


 Compressor High Speed
Compressor Medium Speed


What sort of temp drop can I expect?

The Delta T will be similar to your home. You can expect a 25-30°F temp drop with the compressor running on medium speed. If you require a larger temp drop and would prefer to run the compressor in high speed, you can expect a 30-35°F temp drop.

Will it also function as a heat pump?

No, unfortunately at present there are no 12V reversing valves on the market or controllers that can handle this. Once a 12V reversing valve becomes available we will research and develop a system that can also act as a heat pump.

Can the blower also be used for heat?

Yes! Our new HVAC ducted evaporator has a built in heat coil capable of 25,000BTU/h of heat. Standard 5/8" ports to plumb your hydronic heater. 

If you have any other questions, do not hesitate to email us sales@undermountac.com