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Car Forum / Ford / Ford Trucks / October 2007Air Conditioner issues
My Dad has a '94 Ranger with trouble in the AC system. It has plenty of R134a, but there is no voltage at the connectors of the Low or High Pressure switches, or at the AC clutch itself. The fuse under the dash is good, as is a fuse that is marked as A/C WOT -- I do no tknow what WOT means -- and the AC relay in the relay box clicks on and off. The Owner's Manual states that the AC system will shut off in full throttle operations to send all of the available HP to the drive train instead of letting the AC system rob power. My working theory at this time is that the means of detecting full throttle operation as the AC system is concerned is falsely detecting full throttle. This would account for no power to the pressure switches or to the clutch. I did a continuity check to the clutch and pressure switches, and all showed continuity. The Low Pressure Switch is located by the condensor (a large coffee can shaped cylinder) near the firewall on the passenger side. The High Pressure Switch is mounted to a hose coming out of the compressor, and the compressor itself is obvious. The truck is also having an issue with the transmission that may be related -- if the transmissioin issue is electrical. My Dad reports shifting variations depending upon the truck being warmed up or cold. Perhaps the transmission trouble is really transmission trouble, I do not know and have not experienced the malfunction he thinks exists. Back to the AC, how does the AC system know that the truck is in full throttle operation and shut itself off -- or how does the truck know it is in full throttle operation and disable the AC without affecting a host of other systems controlled by the Throttle Position Sensor? Except for the AC, and perhaps the transmission, there is no other reported problem. The truck is OBD I, and I haven't a scan tool for it, but I'm not certain the scan tool would show this problem. The Check Engine light is not ON. >The fuse under the dash is good, as is >a fuse that is marked as A/C WOT -- I do no tknow what WOT means -- and the >AC relay in the relay box clicks on and off. A/C WOT is a a relay that disables A/C at WOT (Wide Open THrottle). You might check this part of circuit and relay. ----------------- TheSnoMan.com >>The fuse under the dash is good, as is >>a fuse that is marked as A/C WOT -- I do no tknow what WOT means -- and [quoted text clipped - 3 lines] > A/C WOT is a a relay that disables A/C at WOT (Wide Open THrottle). > You might check this part of circuit and relay. We replaced the relay. It is powered any time the ignition is set to ON, even if the motor is not running. If the relay is not supposed to energize until Wide Open Throttle operations exist, then this is the trouble. To test this theory, I can devise a jumper that puts power back onto the contact that is opened when the relay energizes. Power to the clutch (and pressure switches, I assume) passes through the NC contact, but since the contact is opened because the relay is energized, there is no power ... Now, all I have to do is figure out why the relay is powered when the throttle is not wide open. Of course, I could have the whole thing backward, and the relay is powered all of the time until the throttle is wide open, but that would power a relay needlessly for 99% of its life. I like the idea that the relay is not powered until the throttle is held open, this would let the relay remain at rest for normal operations, and only power up for the exception ... Thanks, I can check that. Where does the WOT signal come from? Can it confuse the transmission, but not affect the fuel delivery and associated systems? My dad says that the transmission does not drop into 1st gear when he pulls to a stop sign or light, and this causes the truck begin its next leg of the journey in 2nd gear. He says he can do something (I forget what he does) that will get the truck into 1st, but he says there are other similar kinds of shifting issues that sound as though they have roots in an electrical problem, perhaps the false signal that the truck is already in Wide Open Throttle operation, so the transmission is simply confused and is working properly considering the signals coming to it are faulty. >Now, all I have to do is figure out why the relay is powered when the >throttle is not wide open. [quoted text clipped - 4 lines] >powered until the throttle is held open, this would let the relay remain at >rest for normal operations, and only power up for the exception ... Relay is only supposed to work WOT. Check switch powering it. Also I am not sure if your setup is power always with switched ground for relay coil or grounded always with switched power (GM and Ford swaps around on this switching over model years) If it is always hot with switch ground then it could be a bad switch or a shorted ground wire causing it to ground all the time. A shorted power wire would blow fuse. ----------------- TheSnoMan.com >>> The fuse under the dash is good, as is >>> a fuse that is marked as A/C WOT -- I do no tknow what WOT means -- [quoted text clipped - 38 lines] > simply confused and is working properly considering the signals coming > to it are faulty. >>> The fuse under the dash is good, as is >>> a fuse that is marked as A/C WOT -- I do no tknow what WOT means -- [quoted text clipped - 38 lines] > simply confused and is working properly considering the signals coming > to it are faulty. Many cars use a vacuum switch to detect wide open throttle and suppress the compressor during acceleration. When you floor it the manifold vacuum drops like a rock and the vacuum switch detects this turning off the compressor. The tranny downshift problem may also be vacuum related. I'd start by looking for a vacuum leak as it could explain both problems. Don't over look the vacuum hoses. Ford uses absolute sh.t quality hoses that will crack at the connection point due to the stretching stress. One thing is strange though. Usually a leak of this magnitude will cause a rough idle or at least trigger the check engine light. Do you have either of these problems? > Many cars use a vacuum switch to detect wide open throttle and suppress > the compressor during acceleration. When you floor it the manifold vacuum [quoted text clipped - 6 lines] > rough idle or at least trigger the check engine light. Do you have either > of these problems? No, and it turns out that my brother installed a modulator valve, or some such part, and there was a piece missing. He did not notice the small part for a few days, then apparently found it in the bottom of the box. Anyway, after the part was installed, the transmission issues were resolved. Now, the only remaining trouble is the AC system having no power. The WOT relay is activated, but if I connect a jumper across the NC contacts, the AC clutch still refuses to function. I need a schematic to work this any further. >> Many cars use a vacuum switch to detect wide open throttle and >> suppress the compressor during acceleration. When you floor it the [quoted text clipped - 15 lines] > The WOT relay is activated, but if I connect a jumper across the NC > contacts, the AC clutch still refuses to function. What happens if you disconnect the relay to either deactivate it or disconnect the circuit being controlled by the relay in order to open that circuit? > I need a schematic to work this any further. >>> Many cars use a vacuum switch to detect wide open throttle and suppress >>> the compressor during acceleration. When you floor it the manifold [quoted text clipped - 20 lines] > disconnect the circuit being controlled by the relay in order to open that > circuit? Turns out that the system was so low on juice that it was locked up. My dad took his truck to the professionals and had the AC system serviced. I guess I don't know all that I think I understand, or vice versa, anyway the guy told my dad that if the pressure runs low enough, you can't add juice at home. He had to add through the high pressure port, but when I tried to add at home, I plug into the low pressure port. My guage said the pressure was good, but apparently the system can captivate juice on the low pressure side and isolate it so that no more juice can be added. It took $170 to evacuate the system and refill it, now it runs okay. My diagnosis was that the pressure was good but the electric stuff was whacked, when in reality the electrics werre good but the pressure was whacked. On my Bronco, the AC clutch cycled on very short cycles when it ran low on juice, apparently my dad's Ranger does the same, but he ignored it because the weather allowed him to be comfortable just be rolling the windows down. > Turns out that the system was so low on juice that it was locked up. > > My dad took his truck to the professionals and had the AC system serviced. > I guess I don't know all that I think I understand, or vice versa, anyway > the guy told my dad that if the pressure runs low enough, you can't add > juice at home. Actually, you can. You disconnect and jumper the low pressure connection in the harness, and cycle the compressor, which pulls in the refrigerant on the low pressure (suction) side. Spdloader >> Turns out that the system was so low on juice that it was locked up. >> [quoted text clipped - 8 lines] > > Spdloader I wish you woulda told me that $170 ago. I did a continuity test on the low pressure switch, and it was shorted -- it had continuity -- so it did not occur to me to jumper the pins inside the connector. According to my continuity check, the pins were already being jumpered by the switch itself. >>> Turns out that the system was so low on juice that it was locked up. >>> [quoted text clipped - 15 lines] > the connector. According to my continuity check, the pins were already > being jumpered by the switch itself. Sorry man, I wasn't paying attention to the posts. It is as simple as using a paper clip to jumper the low side connector in the harness to cycle the compressor. You have to be careful and fast with the refrigerant if it's (the freon/oil charge) very low, or damage to the compressor may occur. I'd have responded sooner, but had my head up.........you know the rest. Spdloader The WOT relay has power as soon as the key is turned ON, and the contacts of the have no power on them. They are both ground sources, and jumping them with the relay pulled out does not activate the AC clutch. Does the Ranger have a problem with the life support system that makes the AC shut down? My BMW has a known issue with the Control Module (operator controls) that makes the system shut down. Is there a known problem with the control panel that will make the AC inoperative? When the AC system is activated, the Fan Speed knob is depressed to illuminate a small lamp. The lamp turns ON and OFF as expected, but the AC system does not activate. There is no voltage on any of the electrical connections under the hood -- the High- and Low- pressure switches are cold, the contacts at the WOT relay are also cold. I guess I need a schematic ... > My Dad has a '94 Ranger with trouble in the AC system. It has plenty of > R134a, but there is no voltage at the connectors of the Low or High [quoted text clipped - 29 lines] > The truck is OBD I, and I haven't a scan tool for it, but I'm not certain > the scan tool would show this problem. The Check Engine light is not ON.
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