phamh2000

Hey guys--

I was wondering if it's normal for the air conditioner's compressor (?) to turn on every 10-20 seconds, and then turn off a couple of seconds later. I can feel the engine revving harder when it turns on (making me have to push on the break harder to keep it at a halt) and can also see the rpm go from ~.5 --> .7 --> .4 back to .5 (x1000 rpm). (From .7 --> .4, i can hear the compressor stop, and I suppose the RPM's are just going back to normal).

Is this normal? Last saturday, I converted my system to the new stuff (154?) that costs $19 a lb instead of $47. Does this have anything to do with it? What else can I do?

Thanks!

SC300T

An SC400 compressor doesn't cycle on and off in normal operation as it would on the ES300. When the a/c is on, there will always be a constant pull on the engine in these cars. I assume we're talking about the SC. The ES and RX share the standard (cheaper) Toyota compressors that cycle on/off to keep the core at a certain temp. I believe the SC,LS,GS all feature a variable displacement compressor that doesn't have to cycle on-off to maintain a certain core temp. You shouldn't get any a/c surging in these cars (other than switching the a/c on or off). Audi and VW(Passat) also use this more advanced compressor design.

Perhaps in your conversion process, the system wasn't fully charged or perhaps overcharged.

wwest

AS far as I know Lexus isn't yet using a variable displacement A/C compressor and certainly not as early as this. Some MB vehicles are now using a "swash plate" (think of a helicopter rotor tilt control plate) to vary the travel of the pistons in the A/C compressor.

pham, the cycling on and off is perfectly normal. Your car uses an electromagnetic clutch to engage and disengage the A/C compressor input drive shaft. If the need for cooling is high enough, or the system is undersized, or low on refrigerant (freon or r-134a) the compressor will cycle on more often, remain on for longer periods, or remain on constantly if the need for cooling is extraordinary.

The A/C compressor cycles ON to build up a "reservoir" of liquid refrigerant. Once thee is enough "reserve" a pressure switch opens and the compressor turns off until that switch closes again indicating a need for more liquid refrigerant.

AND.

Your new refrigerant is not nearly as efficient as was the old so the compressor cycling might more often and of a longer duration therefore more noticeable.

strongsail

A short-cycling compressor is usually a sign of a pressure switch turning the compressor off - most systems have low & high pressure switches that protect the compressor. Too much refrigerant can cause saturation and that will trip the high switch - internal icing from moisture in the system will do the same - or not enough refrigerant will trip the low switch. With small systems like auto A/C, even an ounce too much or too little will cause problems - a reason perhaps to have a good shop do the A/C work -

strongsail

another thought - phamh, you said you converted your system - had it been working before? If it had not been working for a while because it had a leak, the internal circuit will equalize with the atmosphere and you will end up with ambient moisture in the circuit, which will cause icing/high pressure/shutdown. Returning a system to service after it's been down for a while normally requires a new filter-dryer and a nitrogen purge, followed by drawing a vacuum before replenishing the refrigerant.

phamh2000

I don't know about the filter or the nitrogen purge (I do remember a step on the machine--maybe the nitrogen purge), but I do remember a "deep vacuum", so I think that was done. It is very possible that he overfilled/underfilled--i think he filled until it wouldn't fill any more, prob not knowing about the pressure switch.

Thanks for all your help!

SC300T

The Compressor on my 92 SC300 doesn't cycle on and off... Call it what you want. Drive an SC and an ES or RX back to back and you'll see what I mean. Early LS400s (had one) are the same way, as is our GS400. It is a variable displacement design on the GS,LS,SC ---no clutch cycling. ES And RX have a standard setup that cycles on and off.