EvilMJ Posted July 23, 2020 Share Posted July 23, 2020 Have the oddest problem. I can be driving with super cold air and stop for 2-3 minutes or even kill it backing up, restart and the the air blows hot! Sometimes I can turn it back off and it starts blowing cold again - sometimes not... wtf?!? Eventually it will get cold again. Anyone else had this problem? Link to comment Share on other sites More sharing options...
EvilMJ Posted July 23, 2020 Author Share Posted July 23, 2020 By turn it off, I mean restart the truck. Flipping AC controls makes no difference. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 23, 2020 Share Posted July 23, 2020 I have the odd experience of the engine being bogged down by the compressor but that’s it. I would check your wiring and the compressor relay and see if it’s going bad. Link to comment Share on other sites More sharing options...
Ωhm Posted July 23, 2020 Share Posted July 23, 2020 If your Evaporator is icing up the Thermostat Switch will shut down AC until icing issues goes away. Link to comment Share on other sites More sharing options...
EvilMJ Posted July 24, 2020 Author Share Posted July 24, 2020 17 hours ago, Ωhm said: If your Evaporator is icing up the Thermostat Switch will shut down AC until icing issues goes away. Might be... but it works perfectly fine, no dragging, cold air. Accidentally kill it for a split second, restart, and air is hot. Makes no sense. Eagle may be right, weak relay or something... dunno. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 25, 2020 Share Posted July 25, 2020 I have the same problem. It seems to be heat related as it only seems to happen on really hot days. The AC compressor clutch won't engage. I have unplugged the wire to the compressor clutch and touched it to the positive battery post and the clutch will engage. If I keep driving the AC will start operating correctly in 5 minutes or so. Is the Thermostat Switch prone to failure or is there a more likely cause? Link to comment Share on other sites More sharing options...
AMC86Kid Posted July 25, 2020 Share Posted July 25, 2020 You need to test the system when it’s blowing hot make sure clutch is engaged and the pressure switch is operating correctly otherwise it’s a wiring issue Link to comment Share on other sites More sharing options...
olddude Posted July 25, 2020 Share Posted July 25, 2020 I had a similar experience. It would be cooling just fine ,then if I stopped for any reason it would quit cooling. It was like I had shut it off. If I put it in neutral and raced the engine it would start cooling again. Found out the compressor was worn out. With the engine running, a/c on you could tap on the compressor with a hammer and it would shut off. Link to comment Share on other sites More sharing options...
MJCARENA Posted July 25, 2020 Share Posted July 25, 2020 1 hour ago, olddude said: I had a similar experience. It would be cooling just fine ,then if I stopped for any reason it would quit cooling. It was like I had shut it off. If I put it in neutral and raced the engine it would start cooling again. Found out the compressor was worn out. With the engine running, a/c on you could tap on the compressor with a hammer and it would shut off. Measure your voltage at the clutch. I had the same problem, AC would turn off at stops and had to rev the engine to kick back on. I only had around 9 volts at idle at the clutch, and when I rev the engine it would go to around 11 volts and the compressor clutch would engage. I could not find where I was dropping the voltage, so I installed a relay between the battery and the compressor clutch with the original clutch wire activating the relay. Never had an issue again. Link to comment Share on other sites More sharing options...
olddude Posted July 25, 2020 Share Posted July 25, 2020 26 minutes ago, MJCARENA said: Measure your voltage at the clutch. I had the same problem, AC would turn off at stops and had to rev the engine to kick back on. I only had around 9 volts at idle at the clutch, and when I rev the engine it would go to around 11 volts and the compressor clutch would engage. I could not find where I was dropping the voltage, so I installed a relay between the battery and the compressor clutch with the original clutch wire activating the relay. Never had an issue again. This was several years ago. I replaced the compressor, works fine now. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 25, 2020 Share Posted July 25, 2020 I have done a little trouble shooting and found that I also have a drop in voltage at the clutch. If I unplug the ax cooling fan then the voltage goes up and the clutch works as it should. I am now going to trouble shoot the power distribution circuit. MJCARENA, I thought of wiring past the original wiring, but I thought I would at last look at the wiring first. oldude, I also thought about the AC clutch and it's windings, clutch gets hot and quits working unless you put more voltage to it Link to comment Share on other sites More sharing options...
AZJeff Posted July 25, 2020 Share Posted July 25, 2020 4 hours ago, OldManComanche said: I have done a little trouble shooting and found that I also have a drop in voltage at the clutch. If I unplug the ax cooling fan then the voltage goes up and the clutch works as it should. I am now going to trouble shoot the power distribution circuit. MJCARENA, I thought of wiring past the original wiring, but I thought I would at last look at the wiring first. oldude, I also thought about the AC clutch and it's windings, clutch gets hot and quits working unless you put more voltage to it The clutch is just a electromagnet whose coil creates the magnetic field when 12V is applied. The fact that applying more voltage makes the clutch work is damnning evidence that the clutch coil is toast. You may or may not be able to obtain just a new clutch assembly, depending on which brand of compressor your MJ has. I am not reallly up to speed on which compressors they used back in the 1980's, so you might have to do some searching on line for a parts source. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 26, 2020 Share Posted July 26, 2020 The AC clutch works as it is supposed to when you first start the truck (cold), but after running for 5/10 minutes (hot) it will not energize if you shut the engine off and restart or turn AC off and back on. I think the clutch windings are OK. As I stated earlier, I can touch the clutch wire to the battery post and the clutch works as it should. I get a blue spark when I do this. When I connect the clutch wire to the wire supplying the clutch I get a VERY faint spark. Voltage at the battery, engine running is 14 voIts, at clutch wire (unplugged) about 11.5 volts. Looks like there is not enough amperage / voltage to engage the clutch. I have cleaned power distribution lugs at the starter relay, wiring connections in the circuit, cleaned the AC relay and socket, low pressure switch. I am in the process of checking wires for resistance and bad diodes. It is just GOOD Fun! Link to comment Share on other sites More sharing options...
Ωhm Posted July 26, 2020 Share Posted July 26, 2020 With ENGINE RUNNING do the following: When AC clutch is ENGAGED measure voltage at D2_6. Should read B+ vdc. When AC clutch is DISENGAGED measure voltage at D2_6. Should read 0vdc. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 26, 2020 Share Posted July 26, 2020 Ohm; I checked (5 times) the voltage at test point D2-6 and got 0 vdc both with clutch engaged and disengaged (clutch works). I see the D2-6 test point on the schematic and should be getting the voltages as you suggest. A little bit of mystery. I think I will let everything cool down and ohm the AC clutch and Aux blower motor. Run the AC till everything is nice and warn and ohm them again and see if there is a difference Link to comment Share on other sites More sharing options...
Ωhm Posted July 26, 2020 Share Posted July 26, 2020 Examine Engine Harness Splice_P. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 26, 2020 Share Posted July 26, 2020 Thank You, I will look for the splice later, it looks to be around the battery somewhere. I am going to take a little break, thermometer in my building is showing 90 degrees in the shade. I ohmed the clutch and fan hot and cold and got about the same readings, so I am not going to worry with them for now. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 29, 2020 Share Posted July 29, 2020 I tried MJCARENA's relay idea. It works great! There just wasn't enough voltage / amperage to make the hot clutch engage going through the original wiring. Thanks OHM for the tips! I was certain that there is a break or poor connection in the wiring. I looked at trying to find the splice P, and decided that when I got done there would be more torn up than what I got fixed. The relay bypasses the wiring problem and I haven't hacked up the wiring harness. I had a relay and some wiring already so it was simple. Link to comment Share on other sites More sharing options...
Ωhm Posted July 29, 2020 Share Posted July 29, 2020 By design when the AC clutch is engaged, the radiator cooling fan will energize (engage). Do you still have this function? Link to comment Share on other sites More sharing options...
OldManComanche Posted July 30, 2020 Share Posted July 30, 2020 The simple answer is Yes. All of the original wiring is still there so the wiring to the fan is not disturbed. I used the wire to the compressor clutch to power the coil of a separate relay (not original one) and grounded the other side so that when you turned on the AC you energized the relay. A separate circuit through the relay contacts ran from the starter relay (Battery +) to the wire from the AC clutch, eliminating the weak original circuit. I used 12 gauge wire in this circuit, a 20 amp fuse between the starter relay and the jeep relay, and wire ends that will plug into the original Jeep wiring. I don't know if many other people are having a problem like this, but this seems to have fixed my problem. I have owned 3 Comanche's with AC. None of them had a working AC system when I got them. All 3 have had a full charge of freon in them. All 3 had AC wiring problems. Thanks again to MJCARENA for the relay idea. Link to comment Share on other sites More sharing options...
MJCARENA Posted July 30, 2020 Share Posted July 30, 2020 I also could not find the problem. So I did that work around. Worked so good I never looked for the issue again. Link to comment Share on other sites More sharing options...
OldManComanche Posted July 31, 2020 Share Posted July 31, 2020 I agree, I hate not doing repairs "correctly"; BUT... I have had a gut full of trying to fix bad wiring. With this work around, if you want AC you flip the switch and the compressor engages, no wait, no problem. (You know what it is like where you are to not have a WORKING AC!) Now it on to the next project! Link to comment Share on other sites More sharing options...
EvilMJ Posted August 19, 2020 Author Share Posted August 19, 2020 On 7/25/2020 at 9:55 AM, OldManComanche said: I have the same problem. It seems to be heat related as it only seems to happen on really hot days. The AC compressor clutch won't engage. I have unplugged the wire to the compressor clutch and touched it to the positive battery post and the clutch will engage. If I keep driving the AC will start operating correctly in 5 minutes or so. Is the Thermostat Switch prone to failure or is there a more likely cause? Sounds about right (sorry for delay - been busy itrw). A weak relay or a cold solder joint may be the culprit with the heat issue. Link to comment Share on other sites More sharing options...
EvilMJ Posted August 19, 2020 Author Share Posted August 19, 2020 On 7/30/2020 at 9:14 AM, OldManComanche said: d grounded the other side so that when you turned on the AC you energized the relay. A separate circuit through the relay contacts ran from the starter relay (Battery +) to the wire from the AC clutch, eliminating the weak original circuit. I used 12 gauge wire in this circuit, a I finally read the rest of the posts, seems like the relay is the way to go. Thanks guys for jumping on this and helping to figure it out! I have a spare relay socket in the console - I know what I'll be doing in my next bit of free time! lol Link to comment Share on other sites More sharing options...
Red Mistress Posted August 20, 2020 Share Posted August 20, 2020 I’m having exact same issue. A/C works until shut off truck. Clutch won’t engage until engine cools off. i suspected weak clutch or clutch gap worn beyond .020 to .030 spec. that Sanden says. May be a combination of factory wiring and worn clutch. Thanks to this thread I know where to start work. Link to comment Share on other sites More sharing options...
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