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AC compressor on and off and on and off

vpcomm92

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Just wondering if this is normal,
On a really hot day, I turn my AC on, the compressor kicks in, and you can hear the relay turning on the engine fan. Then 10 seconds later, fan off, compressor de-clutches, then 10 second later on again. 10 second is a rough estimate but it just keeps going on and off.
Yeah the car cools down, and nothing major happens as a consequence, but the lurching forward when it clutches and declutches and the sudden drop/gains in revs and speed when it does really starts to piss me off eventually.
Normal, or not?

It's a SII VP V6 exec btw
Thanks :)
 

Jxfwsf

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sounds like it's low on gas and the low pressure switch is turning the system off to protect it
(or the other way round and to much gas and the high pressure switch)
i'm thinking low pressure though as my vn was doing similar but not as bad before i topped it up and when a gauge was connected to check the level it started turning on and off in about 5 second intervals with the loss in pressure
 

vpcomm92

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I'd Acrually say the latter coz I had it regassed less than 2 months ago.
But that can't be right coz some days it's fine some days it's not, either way it ends up cool.
Also, it tends to be worse on hot days.
Couldn't have leaked out coz when I had it regassed it still had 650gms left (only 200 lost) since the previous regas in 2006
 

Jxfwsf

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ah so it's had work, try replacing the low pressure switch on the dryer/filter, they have a tendancy to fail and play up like this then
possibly the overheat sensor on the compressor or the high pressure side switch
 

Jxfwsf

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what was it regassed with and what retrofitting work has been done?
 

vpcomm92

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Retrofitted to r134a in 2006 and refills last year with r134a

How do I find/see if they've failed with those sensors?
 

ryan21

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im having the same problem, where is the low pressure switch?
 

Jxfwsf

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low pressure switch in on the filter/dryer.... well it is on the r12 system, round cylinder up near the firewall, when it starts doing it again, unplug the wire going to it and short the plug with a paper clip/piece of wire, if it comes on and doesn't cut out then it's that sensor/switch. If replacing it be quick, there's a valve behind it so you'll lose a small amount of refrigerant, replace the Oring also at the same time, when installing once again be quick, also wear gloves and don't put your face near it, freezer burn is bad.

high pressure switch is up near the condenser, i'll have to go have a look at one to check if it should be open or closed state, but it's usually the lp switch.

DO NOT SHORT THIS OUT PERMANENTLY IT'S THERE FOR A REASON AND SAFETY IF THERE'S A PROB IN THE AC UNIT IT TURNS IT OFF.
 

Jxfwsf

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found another cause for this by accident today.

replaced the rh head light in a car and after i'd finished started it up to align the headlights and heard the ac cycling on and off repeatedly..

first thought was oh crap. I'd just overhauled the system as regassed it a few weeks ago and didn't feel like doing that again as i was sure i'd replaced everything needed.
Started at the lp switch and this wasn't it and then noticed the engine fan wasn't coming on, the plug was in bad shape and when i installed the headlight it had been bumped, fixed this and it's working 100% again.

so check for sufficient airflow through the condenser and radiator and make sure the fan is coming on with the ac.
 
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