87 Aerostar A/C

The A/C on my 87 Aerostar work fine, but it allways shut the compressor off when I'm in a stop and kind of goes on and off continuosly every 4 to 5 seconds while in drive and stoped, but it works fine when I'm moving.
It kind of drive me crazy because it cause the idle to go up and down. Is there any fix for it? ( theA/C system is fully charged).
I will apreciate your help and if you can email me your answers. thanks Ben
snipped-for-privacy@cheloco.com
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Ben wrote:

the compressor clutch is sometimes not working.. on mine it gets electrcitiy( 12 volts to the relay(integrated control relay) and it does not come out with voltage, what controls this is the throttle valve sensor, might need a new on but check it out first... or someother sensor that is telling the relay to not operate as the car is either wide open throttle, too hot, or something else.... like mine its not the charge as when it works its ice cold, but i do find that by giving it a little gas with the foot the a/c works almost all the time.. i changed out all my sensors, will then go into the int. control relay and check that out....
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You're not getting enough airflow thru your condenser, the radiator in front of the engine's radiator. Maybe insects, maybe cooling fan. It could also be low refrigerant or "twitchy" low pressure switch.
Ben wrote:

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Are you suggesting that a 1987 vehicle has a high-pressure cutoff switch? (Which would be the only reason the compressor would be turning on and off due to clogged airflow through the condenser). Clogged airflow through the condenser would raise system pressure, which (I believe) systems of this era isn't even monitor. (R-12 system)
Has this vehicle been legally converted to r-134a (a high-pressure cutoff switch will have been installed if so)?
How do you know the system is full?
IF the idle is going up and down, then I"m assuming the computer is not turning the compressor on and off (or it would also adjust the idle as well, and the idle wouldn't go up and down).
Perhaps it is a loose connection at the compressor? Something that is causing the voltage to the clutch coil to be intermittent. Perhaps at higher speeds you don't notice it as much because the compressor does more work while it is on and the engine is turning it faster.
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The A/C has been doing this for several years, and the solution I found was to increase the RPM to 1000, by opening the trotle with the adjusting screw, but then when I'm not using the A/C, the idle is to hight. There is no intermitent wiring or anything, the airflow is good and it does it all the time ( just turned on, or after awhile), I hear the A/C relay clicking everytime is going on/off, but one thing I don't know is what control this relay? is it the computer or something else? and if it does it at low RPM ( 800 ) what is the correct RPM setting with the A/C on? I was thinking in bypassing the A/C relay and install a thermostat ( like in the old times A/C), but then when I need the extra power like in full trotle, it won't disconect. Any sugestions?
Ben

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Your low-pressure switch is controlling the A/C clutch. The switch may be weak, or you're low on refrigerant, in spite of the fact that the system seems to cool adequately. You could have icing at the evaporator, but it would have to maintain 38 F to keep it in an iced condition. If higher RPM does it for you, the condenser has lost efficiency for some reason, and an electric pusher fan on the front of the condenser could help. Power the fan via a relay from the battery that's triggered by the compressor clutch input, and it still would be automatic operation. The clutch would still cycle, but not as often. Having said all that, the first thing I'd still do is have the charge checked, since you simply may be low on refrigerant.
Ben wrote:

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