AC causing drama...

[ajchetcuti]

Has anybody had an issue with the AC kicking in really affecting the car?

 

If I'm rolling in traffic and the AC kicks back in the car lurches forward and will creep at twice the usual speed. If I'm sat on the brakes the whole car will shudder as the compressor kicks in. Also when braking to a halt the car will suddenly dive when the AC knocks off as there's less force against the braking. It's really annoying and kind of ruins the otherwise smoothness of the LS. Do you think I need a rebuild of the compressor or a replacement? Could it be anything else? Anybody else had this issue? Thanks!

 

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[runsgrateasanut]

The engine of my Car does speed up when A/C kicks in which of course can happen at varying times, especially when the car has reached the correct internal climate temp but if stopped in traffic heat will cause it to kick in.  Normal, I have assumed.

Sounds like you perhaps should check that the compressor is bolted tight if getting a judder. Or could it be to do with the Serpentine belt failing?

Not sure about the braking part but if you are sloing an engine which is high revving and it suddenyl fgoes to lower revving then you won't need so much pressure.  Not felt it mysellf but perhps aggresive driving may create a noticeable dive? 

Sorry no definitive answer as not a mechanic.

[ambermarine]

Alex

The AC will increase revs to about 800rpm the tickover on the LS400 is around 650 so the reaction you are getting is likely due to excessive revs being called for by the compressor. Check what the revs are when the AC starts and stops.

The early model ls400 up to 98 had a compressor that stopped and started as the pressure peaked and waned so this caused fluctuations in revs when driving and was noticable but not to a level you descibe.

The Mark 4 was fitted with a new type of compressor which runs continuely and monitors the peaks and troughs of pressure required.

[runsgrateasanut]

Further thought,  Have you done a diagnostic test?  Not sure if faults with A/C show 

 

Read this thread. http://www.lexls.com/tutorials/intro/codereading.html 

OBD1 not OBD2  

[runsgrateasanut]

On 7/26/2019 at 11:07 AM, ambermarine said:

Alex

The AC will increase revs to about 800rpm the tickover on the LS400 is around 650 so the reaction you are getting is likely due to excessive revs being called for by the compressor. Check what the revs are when the AC starts and stops.

 

Exactly right - as I visited the local tip Thursday and had to queue while they crunched the stuff down - ticked over at 630rpm and when A/C came on it went to perhaps just under 800rpm.  Not noticed any diving but down a slight hill into a 30mph zone with A/C on, does require some breaking.

[ajchetcuti]

Hmm I checked the RPM and it is spot on to what you said as the AC kicks in and out. It seems to be settling the more I use it in the heat. Maybe it was just a bit seized?

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[Newbie1]

Good practice to run air con at periods all year around. This keeps the seals in the piping lubricated and prevents leaks. 

[runsgrateasanut]

2 hours ago, Newbie1 said:

Good practice to run air con at periods all year around. This keeps the seals in the piping lubricated and prevents leaks. 

Absolutely right. I tend to switch it off and on rather a lot but I'd always use it when the engine bay is likely to get extremely hot to ensure it keeps the pipes lubricated. Can't say for sure if the Car has had any trouble with the A/C but certainly not in my ownership and re-gassing should never be necessary unless you've got a leak, I believe.  Any Car for sale that says it needs a re-gas I'd avoid lke the plague having owned a Merc 320S and a Toyota Supra Mk 3 which had no air conditioning and a prohbitive cost to repair.