Turning On A/c Kills Engine

[bongobill]

I have a new to me 88 Comanche. Suddenly it quit running.  Discovered if I turn off air conditioner, it runs fine. Apparently a short kills fire to the fuel pump as soon as air it turned on. (not the blower) but air.  I've had jeep shop search for cause without success. Has anyone experienced a similar problem?

 

Thanks.

[shelbyluvv]

Siezed compressor? try to unplug the electrical connector on the compressor and see if it still does it.

[Eagle]

Siezed compressor? try to unplug the electrical connector on the compressor and see if it still does it.

I was leaning in that direction, too. I can't think of anything else that would do it.

[bongobill]

Thanks.  I'll give that a try.

[Jeep Driver]

I have a new to me 88 Comanche. Suddenly it quit running.  Discovered if I turn off air conditioner, it runs fine. Apparently a short kills fire to the fuel pump as soon as air it turned on. (not the blower) but air.  I've had jeep shop search for cause without success. Has anyone experienced a similar problem?

 

Thanks.

The other two guys are correct.

 

I cannot believe a 'shop' could not figure that out in 5 seconds....????????

[ftpiercecracker1]

You guys really think that a seized compressor would stop an engine cold in its tracks?  :???: I know OP didnt specify which motor he has, but either way; a 2.5 maybe, but a 4.0?  I would be very surprised, i would think the belt would slip long before the engine died. Even if the the compressor circuit did short out the fuel pump circuit, the truck should continue to run for at least a few more seconds and not stall out like someone popped the clutch to quick.

 

 

Unless OP has a 2.5 and has his belt tighter than a banjo string, i just can't imagine the a/c compressor alone providing enough resistance to stop an engine cold. This does not mean it is not possible, I actually hope that is all there is to it. It would make his life a heck of a lot easier, instead of having to chase down a short god knows where.

 

Best of luck OP,

 

 

FPC,

out.

[danbyrambler]

:agree:

 

& way too little info - Engine?  Factory air?  Dies on either AC or Max?  On defrost?  At idle or driving?   Blower speed or temp settings make a dif?  More to the AC than the comp & its clutch - - No engine running means no AC; Is AC charged?  Hj/Low press switches OK? Vacuum OK?  (Wouldn't think vac part of AC selection would cause shut down, much less a sudden one) - -  Aux fan OK?  Even when engine does the sudden thing the aux fan should have come on immediately upon AC selection & will freewheel 4a short time, engine or no- easy enuff to ck - Fast & dirty wi no AC - idle with Blocked rad - Aux fan come on at specked temp?  What temp? Dunno What engine/sensor he's got - - Hard to believe a bonafide Chrysler/Jeep dealer would give up easily, much less pass onna chance to push/sell parts - Go to another shop for a 2nd opinion? - - - - "Apparently a short"- - Huh?  Dunno who's terminology/opinion & generally "shorts" blow fuses/trip breakers/melt things & other probs easy enough to track down, esp for a dealership - Sounds more like ground prob - - Anyway, I'd start with AC system - easy to ck 1st & troubleshoot components one by one - Comp, clutch, fan, fan relay . . . .

[Jeep Driver]

With the engine OFF! all anyone has to do is turn the clutch by hand, the face of the clutch will turn or it will not.

 

If it turns, it's not the compressor, if it does not, the compressor is locked up.

 

It's that simple.

[shelbyluvv]

I want him to unplug the comperssor to see if it still does it so we know if it is a wiring issue or a bad compressor.

 

I have seen a bad idler pulley lock up and engine before.

[88Chief4x4]

Isn't there a relay that idles the engine up when you turn the ac on to help with the extra load? Maybe that relay is bad and when your turning your ac on your idle is to low to start/ keep running

[ftpiercecracker1]

Isn't there a relay that idles the engine up when you turn the ac on to help with the extra load? Maybe that relay is bad and when your turning your ac on your idle is to low to start/ keep running

 

 

That is what mine does, turn the a/c on and the idle drops dramatically. You can hear the engine struggling.

 

 

I don't think there is such a relay, for the a/c at least. Some MJs/XJs had an 'extended idle' switch, can't remember why at the moment, but it wasnt for the a/c i know that much.

 

I was under the impression that when you turned the a/c on the computer would sense the extra load on the engine and compensate accordingly, but i really don't know TBH.

[Jeep Driver]

 

Isn't there a relay that idles the engine up when you turn the ac on to help with the extra load? Maybe that relay is bad and when your turning your ac on your idle is to low to start/ keep running

 

 

That is what mine does, turn the a/c on and the idle drops dramatically. You can hear the engine struggling.

 

 

I don't think there is such a relay, for the a/c at least. Some MJs/XJs had an 'extended idle' switch, can't remember why at the moment, but it wasnt for the a/c i know that much.

 

I was under the impression that when you turned the a/c on the computer would sense the extra load on the engine and compensate accordingly, but i really don't know TBH.

 

I believe  it was the police units that had the switch so the alt could pick up the extra demand on the battery........lights....radio......computer........etc.......