The Two Main Types of No-Idle Truck Air Conditioners
If you've decided to go no-idle, smart move, the next question is which type of DC air conditioner is right for your truck. The two main options are rooftop units and split systems, and the right choice depends on your cab size, install situation, budget, and how you use your truck.
This guide walks through every factor so you can make the right call — and points you to the specific B-Cool model that fits each scenario.
Rooftop AC Units: Overview
A rooftop DC air conditioner mounts on top of the cab, similar to a traditional diesel APU or RV rooftop unit. The entire system — compressor, condenser, and evaporator — is in one self-contained housing. Air is distributed through a ceiling duct or directly into the cab through a roof opening.
Pros of Rooftop Units
- Single mounting point — simpler roof penetration
- No interior space used for components
- Clean, professional look from outside the truck
- Ideal for standard sleeper cabs with flat roof sections
Cons of Rooftop Units
- Higher roof profile — may affect clearance in some facilities
- Heavier single unit to lift and mount
- Less flexible placement if roof space is limited
Best B-Cool Rooftop Models
5RM — Our most popular rooftop unit for standard sleeper cabs. Available in 12V and 24V. Ideal for Kenworth T680, Freightliner Cascadia, and Peterbilt 579 with 72–76" sleepers.
6RM — Higher capacity rooftop for larger sleepers or hotter climates. Recommended for 80"+ sleepers or drivers in the US Southwest and Central Valley.
Split System AC Units: Overview
A split system separates the condenser (outside the cab, typically mounted on the back wall or under the bunk) from the evaporator (inside the cab). The two units are connected by refrigerant lines that pass through a small hole in the cab wall.
Pros of Split Systems
- More flexible placement — condenser can go on the back wall, frame rail, or toolbox
- Lower roof profile — no rooftop mounting required
- Quieter inside the cab (compressor is outside)
- Easier to install on trucks with curved or complex roof shapes
Cons of Split Systems
- Two mounting points instead of one
- Refrigerant line routing requires planning
- Condenser exposed to road debris (requires protective placement)
Best B-Cool Split System Models
FLEX ST (Standard Connect) — Full split system with field-charged refrigerant lines. Maximum flexibility for custom installs. Available in 12V and 24V.
FLEX QC (Quick Connect) — Pre-charged refrigerant lines for faster installation. No HVAC technician required for the refrigerant connection. Ideal for owner-operators doing their own install.
WMB ST / WMB QC — Wall-mount evaporator variants. Ideal for trucks where a ceiling-mount evaporator isn't practical, including some cab-over configurations and heavy equipment cabs.
How to Choose: Decision Framework
Cab Size
- Standard 72" sleeper — 5RM rooftop or FLEX ST split
- Large 80"+ sleeper — 6RM rooftop or FLEX ST split
- Day cab or small sleeper — FLEX QC or WMB QC split
Install Complexity
- Want the simplest install? — FLEX QC (pre-charged, no HVAC tech needed)
- Have a shop doing the install? — Any model works; FLEX ST gives maximum flexibility
- Doing it yourself? — FLEX QC or 5RM with our install guide
Budget
- Entry point — FLEX QC split system
- Mid-range — 5RM rooftop or FLEX ST split
- Maximum cooling capacity — 6RM rooftop
Use Case
- Long-haul sleeper comfort — 5RM or 6RM rooftop
- Owner-operator DIY install — FLEX QC
- Fleet standardization — FLEX ST (easiest to service)
- Unusual cab shape or heavy equipment — WMB ST or WMB QC
Frequently Asked Questions
Can I use a rooftop unit on a day cab?
Yes, but most day cab drivers prefer a split system because the condenser can be mounted on the back wall without taking up roof space. The FLEX QC is the most popular choice for day cabs.
Which type is quieter inside the cab?
Split systems are generally quieter inside because the compressor (the loudest component) is mounted outside the cab. Rooftop units are still quiet by truck standards, but the compressor is directly above the sleeping area.
Do both types work with solar?
Yes. All B-Cool units are DC-powered and compatible with solar charging systems. A properly sized battery bank with solar top-up can run a B-Cool unit all night with zero engine runtime.
Not sure which unit fits your specific truck? Browse the full B-Cool lineup or contact us for a fitment recommendation.
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