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quick question about idling

menace on Sun July 20, 2008 5:38 PM User is offline

Year: 1992
Make: lexus
Model: sc300
Engine Size: i6
Refrigerant Type: r135
Country of Origin: United States

i just got my ac fixed again. last year had to replace the compressor and then found out i had a leak then fixed the leaked this year. well finally the it seems to be working great driving around highway and street. the problem i seem to have is at idle it seems to blow ambient air. i hear the clutch engaging and disenaging every few seconds. but when driving its perfect. is my idle to low or something. the mechanic said my compressor was weak thats why it doesn't cool when idled. it doesn't seem weak when i'm driving around. its alot better than before i hardly sit at my car idle expect in traffic. any idea. idle seems to be around 800 i guess when it goes about 1000 rpm it works fine

Chick on Sun July 20, 2008 5:47 PM User is offlineView users profile

sounds like an air flow problem, that car uses a fan clutch on the engine fan doesn't it?? Might be time to change it.. Make sure the electric fan in front of the condenser(if equipped) is also working when the ac is turned on.... Hope this helps..

Email: Chick


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mk378 on Sun July 20, 2008 6:05 PM User is offline

If you can press the gas very slightly and it stops cycling, the idle is too low (an engine problem, not an A/C problem). If it keeps doing it look at the fan situation like Chick said.

menace on Mon July 21, 2008 1:02 AM User is offline

fan clutch? there is a fan in front of the engine. i think its being powered by belt. i will look into thanks how much do u think it will cost to replace.

Edited: Mon July 21, 2008 at 1:13 AM by menace

NickD on Mon July 21, 2008 8:51 AM User is offline

What kind of refrigerant is r135? This car came with R-12. Since the Lexus is a very rare vehicle in my neck of the woods, really haven't played with one nor have read anything on R-134a conversions. Problem with R-134a especially in the more complex MVAC systems, you cannot jam enough of it in with the less efficient R-12 condensers, so the low pressure side drops at idle giving cycling problems just like you are reporting.

So what is the whole story on your refrigerant, and also good to post pressures at both 2,000 engine rpm and at idle, that tells a lot.

menace on Mon July 21, 2008 11:32 AM User is offline

i meant r134 i got it retrofitted.

NickD on Mon July 21, 2008 12:11 PM User is offline

What do you guys think about an Lexus converted to R-134a with cooling problems at idle? Any experience with these conversions? Aren't these cars like the Toyota with a TXV and an evaporator thermal cycling switch? Course, can also be cycling on the high side, kind of hard to guess without pressure readings. But you know me, like to stick with R-12 for R-12 systems, Gore hates me.

bohica2xo on Mon July 21, 2008 1:44 PM User is offline

I always tell Lexus owners to keep it the way it was designed... Some Lexus models have a POA valve - (the one in this thread does not) and retrofitting one of those never goes well.

This is a TXV system with a thermistor in the evaporator core.

First, you should run the self diagnostics on the A/C system. The A/C panel will flash two digit trouble codes for many parts of that system.

Second, any further diagnosis will require pressure readings from both the high side & low side - at both idle & 1500 to 2500 engine rpm.

Across the internet, it would appear that the system is cycling on the HPCO when stopped. A total guess without pressures readings however.


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