The slack economy and low sales have caused Cummins Inc. to drop its ComfortGuard auxiliary power unit, but it will continue to honor warranties for those in use and support them indefinitely with parts and service.

The company could not sell enough of the APUs to support the business unit charged with building and marketing them, executives explained.

Another economy related factor is lower fuel prices since last summer. That has have weakened the appeal of APUs, which power on-board "hotel" accessories and cut main-engine idling, reducing fuel use. Cummins said it might return to the APU market if conditions change.

Cummins introduced the ComfortGuard in late 2006. The product combined the generator expertise of the company's Onan brand with tailored HVAC components to power hotel loads, while ts plug-and-play design reduced the cost of installation.