Originally Posted By: 440Magnum
Originally Posted By: nthach
Newer cars use variable-displacement compressors - GM was first to have them.
Variable-displacement compressors are a tiny fraction of the market. Good idea in theory, but very little or no real benefit in practice and a lot of downside (reliability, or more precisely lack thereof). Thermal expansion valves and EPR valves that effectively reduce the load on a fixed-volume compressor effectively achieve the same goal and do so more reliably. Electric compressors will replace the fixed-displacement compressor long before variable-displacement becomes dominant in the marketplace, IMO.
Well, Toyota has implemented them on the hybrids -- actually, they did so about a decade ago. Yes, that would be a relatively small slice of the overall market, but reliability has not been an issue. Our 04 Prius is pumping arctic air just as it was on Day One. And in this application, there is a huge benefit as compared to a compressor that is strictly an ON-OFF design. Rather than imposing a full load (mechanical or electrical) whenever it's on, the design draws only enough current to drive the compressor at a level sufficient to maintain the desired temps. It's a clever design that draws only enough current to do the job, leaving as much of the TB charge as possible for moving the car.
Originally Posted By: nthach
Newer cars use variable-displacement compressors - GM was first to have them.
Variable-displacement compressors are a tiny fraction of the market. Good idea in theory, but very little or no real benefit in practice and a lot of downside (reliability, or more precisely lack thereof). Thermal expansion valves and EPR valves that effectively reduce the load on a fixed-volume compressor effectively achieve the same goal and do so more reliably. Electric compressors will replace the fixed-displacement compressor long before variable-displacement becomes dominant in the marketplace, IMO.
Well, Toyota has implemented them on the hybrids -- actually, they did so about a decade ago. Yes, that would be a relatively small slice of the overall market, but reliability has not been an issue. Our 04 Prius is pumping arctic air just as it was on Day One. And in this application, there is a huge benefit as compared to a compressor that is strictly an ON-OFF design. Rather than imposing a full load (mechanical or electrical) whenever it's on, the design draws only enough current to drive the compressor at a level sufficient to maintain the desired temps. It's a clever design that draws only enough current to do the job, leaving as much of the TB charge as possible for moving the car.
