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Discussion Starter #21
OK, that eliminates a 'hard' ground fault like the wiring between the computer and the PDC or the PDC shorting the relay coil to ground.

I'm still suspecting the computer but have you tried pulling the low pressure plug on the expansion valve (silver valve discussed earlier) to see if the compressor kicks off?
I unplugged the 2 wire connector and the compressor shut off with the AC 'on'. Plugged it back in (compressor kicked back on) then disconnected/reconnected the 3 wire pigtail, same results.
 

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I unplugged the 2 wire connector and the compressor shut off with the AC 'on'. Plugged it back in (compressor kicked back on) then disconnected/reconnected the 3 wire pigtail, same results.
OK, that is interesting and it appears that part of the system is working. At this point, I would be temped to force the high speed fan to stay on by putting a jumper between contacts #30 & 87 in the condenser fan relay socket. That is the relay switched side and shoud force the fan to stay on. Connect up a set of gauges and monitor the system. Perhaps the system is actually low on refrigerant and the fans are kicking off as your high pressure drops below a certain thresehold. I still don't understand why the compressor is not cycling, but there may have been some design changes in 1994 that allow the compressor to run without the fans on when the high side drops below a certain pressure.

If you add refrigerant, monitor your high side to insure you never get much above 350 -375 PSI (assuming it is very hot outside). The condenser fan should be running and you should try to get your engine speed up to about 1200 RPM. I just put a piece of cardbosrd in the throttle stop to get the RPMs up when charging. Remove it when you are done.
 

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Discussion Starter #23
OK, that is interesting and it appears that part of the system is working. At this point, I would be temped to force the high speed fan to stay on by putting a jumper between contacts #30 & 87 in the condenser fan relay socket. That is the relay switched side and shoud force the fan to stay on. Connect up a set of gauges and monitor the system. Perhaps the system is actually low on refrigerant and the fans are kicking off as your high pressure drops below a certain thresehold. I still don't understand why the compressor is not cycling, but there may have been some design changes in 1994 that allow the compressor to run without the fans on when the high side drops below a certain pressure.

If you add refrigerant, monitor your high side to insure you never get much above 350 -375 PSI (assuming it is very hot outside). The condenser fan should be running and you should try to get your engine speed up to about 1200 RPM. I just put a piece of cardbosrd in the throttle stop to get the RPMs up when charging. Remove it when you are done.
Does 110F+ ambient temperature qualify as 'very hot'? :)
 

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Does 110F+ ambient temperature qualify as 'very hot'? :)
uh huh

When I drove up i 95 through S Carolina, N Carolina, and VA on June 29th this year, temps on the vehicle outside thermometer would vary from 105 to 110. The minivan AC kept the front of the vehicle at about 82 (comfortable but not freezing). The air coming out of the center duct showed about 58-60 with the fan on next to high (high is too noisy for me). Since I have no rear air, I expect it might have been uncomfortable in the back of the van at mid day.

Some day I would like to see the entire wiring/control scheme for your 94 mini's AC circuitry. I wonder if the fan circuit for the AC is triggered off a seperate pressure transducer in the high side pressure line. If it is, that could explain some things. I'm beginning to think that your system might be a bit undercharged... or the pressure transducer (if equipped) could be malfunctioning.
 

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I posted earlier that 94 fan control is from a pressure switch on the high side. But that signal then goes to the SMEC which in turn picks up one of the fan relays. There is nothing wrong with the fan cycling in moderate temperatures. If the fan is cycling when its 110 then the A/C isn't making nearly enough high side pressure. Maybe hasn't been testing with 12-1500 rpm which it takes to get full cooling. I often use a screwdriver between the throttle stop and lever, but your cardboard would work fine too.
 

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I posted earlier that 94 fan control is from a pressure switch on the high side. But that signal then goes to the SMEC which in turn picks up one of the fan relays. There is nothing wrong with the fan cycling in moderate temperatures. If the fan is cycling when its 110 then the A/C isn't making nearly enough high side pressure. Maybe hasn't been testing with 12-1500 rpm which it takes to get full cooling. I often use a screwdriver between the throttle stop and lever, but your cardboard would work fine too.
I think adding some refrigerant with a gauge set monitoring pressures should be the next step (that is what KOG is hinting, as well).
 

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Discussion Starter #27
UPDATE:

Since no one at work was able to figure out why the rad fan kept cycling on and off: I said 'the heck with it', went to Pep Boys and bought a 12 oz can of R134 and a hose to dump it into the low side of my AC system. Lo and Behold: the fan stayed on continuously and the dash vents actually blew out cool air. I don't know if I'm under or over charged but, at least I now have some semblance of AC.
 

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UPDATE:

Since no one at work was able to figure out why the rad fan kept cycling on and off: I said 'the heck with it', went to Pep Boys and bought a 12 oz can of R134 and a hose to dump it into the low side of my AC system. Lo and Behold: the fan stayed on continuously and the dash vents actually blew out cool air. I don't know if I'm under or over charged but, at least I now have some semblance of AC.
KOG nailed it when he described the high pressure fan control switch. When Chrysler re-designed the fan control circuit, they used a pressure switch on the AC high side line to turn on the condenser fans instead the old system that locked the fans on solid whenever the compressor was engaged.

You were undercharged and it appears that when the high side pressure went below about 180 PSI, that pressure switch opened and turned the fans off. I'm not sure what the reasoning was behind this design change, other than to save a miniscule amount of energy by not having the fans kick in for a few seconds while pressure builds. Perhaps it is easier on the electrical system by not having all the stuff coming on at the same time.

If your cooling is sufficient, don't do anything. If you want to chance adding more refrigerant, get gauges on it so you don't overcharge it.

Anyhow, it was a long discussion getting to this point, but I think a few of us learned a little bit more about the 94 fan design circuit. I hope the new refrigerant stays in there for a long time. :)
 
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Discussion Starter #29
KOG nailed it when he described the high pressure fan control switch. When Chrysler re-designed the fan control circuit, they used a pressure switch on the AC high side line to turn on the condenser fans instead the old system that locked the fans on solid whenever the compressor was engaged.

You were undercharged and it appears that when the high side pressure went below about 180 PSI, that pressure switch opened and turned the fans off. I'm not sure what the reasoning was behind this design change, other than to save a miniscule amount of energy by not having the fans kick in for a few seconds while pressure builds. Perhaps it is easier on the electrical system by not having all the stuff coming on at the same time.

If your cooling is sufficient, don't do anything. If you want to chance adding more refrigerant, get gauges on it so you don't overcharge it.

Anyhow, it was a long discussion getting to this point, but I think a few of us learned a little bit more about the 94 fan design circuit. I hope the new refrigerant stays in there for a long time. :)
AC def works better: a BIG thanks to both you and KOG. :D
 
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