Truck is a 1986 Ranger 2.9 4x4 super cab, formerly a4ld now C4, with my '88's computer. The a/c is fully charged, and the a/c in my '88 worked fine with it's computer. If i turn the a/c on (with key on) nothing happens, but if i give power temprarily or consistantly to a small red wire (there's 2 red ones) on a relay on the right side firewall that's black, the a/c will work for at least a few minutes, unless i leave the wire jumped then it stays on till it's turned off. Or if the key is off and i turn the a/c on then turn the key on i can here the clutch turn on for about 1 sec then it turns off. The low pressure switch is not the problem either. Any ideas on this one? and good luck to all that give it a try. It has me stumped. and thanks for any help.
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a/c clutch only turns on when relay is temporarily jumped
- Thread starter blue83ranger
- Start date
Check you tps plug. Mine wasn't plugged in all the way and it kept it from working.
I checked for codes and didn't get a tps code but I will check the plug, thanks for the suggestion.
Yeah I didnt get any either, but the ac needs that reading cause it shuts off at WOT.
kimcrwbr1
Well-Known Member
I believe the relay is the WOT wide open throttle relay and is controlled by the computer maybe the relay is getting weak or a connector needs to be cleaned
kimcrwbr1
Well-Known Member
look in the end of the relay connector and see if the female connectors are pushed all the way in put it together and take a small screwdriver or ice pick and push the connectors all the way in.
I'll check both plugs in the morning and i'll let you know how things look.
I asked a guy who is very knowledgable about ac components and this is what he said. I know he is long winded, but I hope something in there helps.
"I don't think that the AC was fed through the computer on OBD1 vehicles. That's likely not the problem. Something is wrong with the wiring though.
The power ON for the AC runs through the switches in the dash, then goes through the HP switch and LP switches on the system before it ends up on the coils of the relay. On the relay itself- all standard relays are both normally open, and normally closed- when power is applied to the coils on the relay through all these switches, it closes the contacts on the compressor clutch which is a high current device. That's why the wire is burning up, it can't handle the current from the AC clutch. You should first check the AC fuse, and then the AC diode. You should get electrical continuity through the diode in one direction only. Now, check out the relay diagram and pull the relay so you can match up the pins to the appropriate wires. You should be able to jump the relay out by jumping the constant hot from the big wire to one side of the coils. This bypasses all the safety controls. If it does not work like this, then something is wrong with the relay- an evil coincidence. You can swap this relay out for a headlight relay if that is the case, these should be the same relay.
I suggest this only because it sounds like he's jumping the wrong wires because the wire is burning up. You only need to provide power to the coils, then the relay will do it's job. If it's not doing it's job, then it's the problem. Now if it does it's job, I'd cut it off really quickly after that. Something is amiss somewhere. It's time to test both the HP and LP switches. With the AC off, both these switches should read electrical continuity. If not, then one is likely bad- or the system is horribly over charged, and the HP relay is doing it's job. Yes I know, the system was working before, but that doesn't mean that the orifice tube didn't finally clog itself up right before you swapped things around. Evil coincidences happen like that which is why we test things instead of assuming.
He needs a set of gauges if nothing can be found to be wrong with the relay itself just to be sure that the HP switch is not doing it's job for a reason. The reason I think it's the HP switch is because the compressor is coming on when he doesn't have it jumped out. If the switch was bad- no continuity ever- then the system would not come on at all. If the LP switch was bad, it would not come on at all, and wouldn't come on if the system's pressure was too low. I think what we have here is either a clogged orifice tube, or a possibly bad compressor.
Gauges will tell the truth of the matter. He's at the end of his knowledge with what he's done, so it's time to try something different. He could partially discharge the system and see if he could get it to run for longer, but that would only tell him that there is definitely something wrong mechanically- ie, clogged orifice tube. He could also just tear the system down, flush the components with mineral spirits and compressed air, then recharge with oil and refrigerant after replacing all the O-rings and orifice tube. He'd need gauges for that also.
I would run a lot of tests to be sure what I thought was going on was what was going on. Double check everything- even if you think, oh that can't happen."
"I don't think that the AC was fed through the computer on OBD1 vehicles. That's likely not the problem. Something is wrong with the wiring though.
The power ON for the AC runs through the switches in the dash, then goes through the HP switch and LP switches on the system before it ends up on the coils of the relay. On the relay itself- all standard relays are both normally open, and normally closed- when power is applied to the coils on the relay through all these switches, it closes the contacts on the compressor clutch which is a high current device. That's why the wire is burning up, it can't handle the current from the AC clutch. You should first check the AC fuse, and then the AC diode. You should get electrical continuity through the diode in one direction only. Now, check out the relay diagram and pull the relay so you can match up the pins to the appropriate wires. You should be able to jump the relay out by jumping the constant hot from the big wire to one side of the coils. This bypasses all the safety controls. If it does not work like this, then something is wrong with the relay- an evil coincidence. You can swap this relay out for a headlight relay if that is the case, these should be the same relay.
I suggest this only because it sounds like he's jumping the wrong wires because the wire is burning up. You only need to provide power to the coils, then the relay will do it's job. If it's not doing it's job, then it's the problem. Now if it does it's job, I'd cut it off really quickly after that. Something is amiss somewhere. It's time to test both the HP and LP switches. With the AC off, both these switches should read electrical continuity. If not, then one is likely bad- or the system is horribly over charged, and the HP relay is doing it's job. Yes I know, the system was working before, but that doesn't mean that the orifice tube didn't finally clog itself up right before you swapped things around. Evil coincidences happen like that which is why we test things instead of assuming.
He needs a set of gauges if nothing can be found to be wrong with the relay itself just to be sure that the HP switch is not doing it's job for a reason. The reason I think it's the HP switch is because the compressor is coming on when he doesn't have it jumped out. If the switch was bad- no continuity ever- then the system would not come on at all. If the LP switch was bad, it would not come on at all, and wouldn't come on if the system's pressure was too low. I think what we have here is either a clogged orifice tube, or a possibly bad compressor.
Gauges will tell the truth of the matter. He's at the end of his knowledge with what he's done, so it's time to try something different. He could partially discharge the system and see if he could get it to run for longer, but that would only tell him that there is definitely something wrong mechanically- ie, clogged orifice tube. He could also just tear the system down, flush the components with mineral spirits and compressed air, then recharge with oil and refrigerant after replacing all the O-rings and orifice tube. He'd need gauges for that also.
I would run a lot of tests to be sure what I thought was going on was what was going on. Double check everything- even if you think, oh that can't happen."
thanks for all that info. i'll check things out like he described. But we actually just filled the a/c, i have a slow leak and there wasn't enough to turn on the clutch at all, so we jumped that relay to at least get it semi going again. And it was put in by someone who is certified to do so.
I checked out the 2 plugs mentioned earlier and they look good. and i used an ohm meter on the tps plug and it's getting connection and the sensor itself is pretty new.
Something else i found out is that with everything off and i turn on the a/c, then very very slowly turn the key on the a/c clutch will turn on and stay on, but it's before anything else gets power, and if i keep turning the key so everything else turns on the a/c clutch turns off. I'll try to check out the ignition switch just to see what i can see.
I checked out the 2 plugs mentioned earlier and they look good. and i used an ohm meter on the tps plug and it's getting connection and the sensor itself is pretty new.
Something else i found out is that with everything off and i turn on the a/c, then very very slowly turn the key on the a/c clutch will turn on and stay on, but it's before anything else gets power, and if i keep turning the key so everything else turns on the a/c clutch turns off. I'll try to check out the ignition switch just to see what i can see.
well, i looked over the ignition switch and it's not the problem. and i can plainly see that the a/c wiring runs out of the cab and goes through the relay then the high pressure switch, and unless the high pressure switch is the low pressure as well there is no high pressure switch. There's just a high pressure relief valve with no place for wires to hook to.
I narrowed down my problem to the WOT relay, ist's shutting down the power to the clutch. Any idea how to fix it?
That doesn't sound right. If thats your problem, then you would have a problem with your alternator, which also shuts off at WOT.
kimcrwbr1
Well-Known Member
Maybe somthing with the computer it controls the relay when it gets a wide open voltage from the TPS it switches the compressor off did you check the voltage coming from the tps or the resistance when you open the throttle the resistance should make the needle sweep smooth any jumping the tps is bad. To measure voltage with it plugged in key on you should have 5 volts at the blk/wht wire and .9v with the throttle closed at the dk green wire as you open the throttle the volts should rise steady up to almos 5 volt on the dk green and drop steady on the other. If the TPS checks out and the relay is good and there are no wires shorted or broken it may be the computer telling the compressor to stay off. You coud either get a good schematic for your system and test the wires from the computer to the solenoid or possibly just wire a switch you can shut it off an on manually using the relay. I still think it is the TPS not giving the signal it needs or the computer. Try and find another TPS/computer at the bone yard for cheap just make sure it has the same engine tranny with a/c.
I will check the tps, but I'm not sure when i will. I also did some searching and i found a site where a mechanic was working on a car, it was either a Lincoln or mercury with the same problem and he couldn't figure it out. so just because the owner needed his car back the guy just unhooked the wire to the relay so the a/c would work. So temporarily that's what i did and the a/c works great. I'll still get the tps checked out as soon as i can so i can actually get this fixed properly. and i have access to 3 different 2.9 computers, I'll see if any gets the relay working right. also on the same topic of that mechanic, one guy suggested that especially on 2.9 rangers if the idle control motor isn't letting the engine idle at the right speed or if the timing is to far off he's seen that be the cause of this. Ever here of that?
I finally got around to checking the TPS. mine was labeled ABC so i didn't write down what color wire i checked if you need the color i can figure it out and i checked the sensor unpluged. The truck side of the plug with the key on C read 4.9 volts, and A and B show nothing. Then the actual TPS A and C read 3.59 ohms at idle and wide open it had no change. B and C 3.48 at idle and .39 wide open. and A and B .63 at idle and wide open 3.67
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