it's that time of the year again.

dksob81 · #1 06-07-2008, 05:00 PM

98 Jeep Grand Cherokee 5.9Limited.

Last year after figuring out that my Orifice tube was bad I replaced it and got my A/C working great but after about 1 - 1 1/2 months it would stop working I would top it off and it would work again for a while, so I knew I had a leak but couldn't find any signs, put die in the system after I did the orifice tube/expansion valve, so I figured it was ol faithful (Evaporator Core), so thursday I began tearing her apart, got it back together yesterday, had to wait for the evap core to come. I replaced the Evaporator core and heater core while I was in there, Drier, and condensor.

When I got to work this morning I vacuumed the system down and and it held vacuum for quite some time, great no leaks, so I began charging the system. well out A/C Machine quit adding freon stopped with a lil over a pound in the systembecause the pressure was getting to high, then, I noticed the A/C Compressor Clutches weren't engaging. checked for power at the compressor had none, jumped the low pressure switch NO GO, jumped the high pressure switch NO GO. then I started testing swapped relay, tested the relay, checked the circuits from the PCM to the Relay (PDC), Circuit from relay (PDC) to compressor. all seems fine. When I ran a jumper wire straight from the battery to the compressor it would kick (engage) but no spin, like it was seized up. well I sucked everything back out while i was at work- just in case I had to tear anything apart. then when I got home I monkey'd around with jumping the compressor straight to the battery. and after a few times kicking on and off it finally broke loose and spins fine now, but that doesn't explain why I wasn't getting any power to the compressor for it to spin.

any ideas?

dksob81 · #2 06-07-2008, 06:14 PM

also on my 5.9Limited there are 2 high pressure sensors on the discharge (pressure) line going from the compressor to the condensor, but there is no plug for the other sensor and I don't ever remember unplugging it for any reason. anyone know what this is about?

xj31 · #3 06-08-2008, 03:45 PM

Do you still have the stock electric fan?5.9s have extra stuff since they have an electric fan.

dksob81 · #4 06-08-2008, 08:03 PM

I don't have the stock electric fan, when I got this jeep a year and a half ago, I had a problem with the jeep overheating with the A/C on and sitting in traffic or whatever the temp would climb, well I traced it to the fan that was in the jeep (was not stock the last owner must have replaced it. well the fan they used was a curved edge (directional) fan which wasn't as efficient with pulling air as it was at blowing air, so I replaced it with another fan of the same size but a straight edge (bi-directiona) and that took care of that problem. didn't have a problem with the overheating after that.

dksob81 · #5 06-08-2008, 09:56 PM

When you turn the A/C on, what tells the PCM when to engage the compressor? I don't see anything linking the ATC (Automatic Temp Control) to the PCM.

xj31 · #6 06-10-2008, 07:48 AM

The ac select is an input to the bcm and from there it is bussed to the pcm.

dksob81 · #7 06-10-2008, 02:12 PM

what do you mean by bussed into the PCM, For some reason I think my problem lies between the BCM and the PCM.

xj31 · #8 06-10-2008, 07:05 PM

You're killing me.My memory on those old ones is not that great but I'll try to explain.Bus means data bus,in your case it's called pci bus.You might notice that there are purple and white wires in a lot of places on your jeep that are twisted together.Thats the pci bus wires.They are for communication.It makes more sense to wire a component or sensor or switch to the closest module and then transmit its data,value ,reading or whatever to any other modules that need the info.An example is your oil gauge.The sending unit is not wired to the dash cluster.Its wired to the pcm then the pcm sends it to the dash.the temp gauge is like that also.I think the fuel gauge is too but I'm not 100% sure.Well the ac select is sent from the control head to the bcm.The bcm sends it over the bus to the pcm.A bus can handle a lot of different switches sensors or whatever because everything sends a different signal or voltage and they can all be sent over the same wires.Pci bus is actually primitive.Can bus is a lot better/faster.I don't know if this is accurate to say for pci bus,but in chrysler vehicles that are can bus,the modules are actually networked.I hope that helps.

xj31 · #9 06-10-2008, 07:07 PM

By the way ,is the ac working now ?

dksob81 · #10 06-11-2008, 05:45 AM

Ok, well I knew what BUS is, I didn't know what you meant by they are bussed together tho. and I see there was only 2 bus wires going from the BCM to the PCM but it doesn't say what the wires were for - so i was a little confused. But with the different voltage signals - I understand now.

No, it's not working, my pressures were high when I jumped the Compressor to get it to kick on, so I think I may have a problem with my Orifice Tube/Liquid Line again.

Thanks for explaining the bus to me.

dksob81 · #11 06-14-2008, 12:58 PM

I figured it out, the other high pressure switch harness is part of the altenator harness and was tucked down under the altenator, must have stuck it there when I did the head gaskets back in march. It's working good now.

reekor · #12 06-14-2008, 07:48 PM

I also have a evaporator core leak. Do you need to take the dash right out to change the evaporator core or will pulling the dash back give me enought room to change it, I'm changing the heater core also.

dksob81 · #13 06-15-2008, 06:20 PM

well you don't have to take it completely out of the jeep but it does have to be completely removed from the firewall.

I have a pretty good write up that I put together the other day for another guy. If you want a copy of it, email me.

Joe
[email protected]

dksob81 · #14 06-15-2008, 06:40 PM

I also have a good evaporator core NEW, well slightly used for 1 week, well technically it wasn't used but for 1 day. I charged the system and put die in the system but then after about a day of messing around with trying the get the compressor to kick on I decharged the system but I noticed it was low again and thought I damaged the evap core when I put it together but my leak was coming from the high side shrader valve. Well I put the new evap core in anyways because I had to pay for it because it was a special order and the other one was a different design,the core was the same design plate fin type but the tubes were slightly different one had a loop in it. but was still a perfect fit. The Evap Core will fit any ZJ 95 - 98 and maybe earlier models as well.

reekor · #15 06-17-2008, 12:22 PM

I have already bought everything at prices that can't be beat.

Compressor $150
Evap $47
Heater core $60
Condenser $59
Liquid line $25
Dryer $20

The only part that i am missing is the discharge line for some reason they dont carry it.

Quote:

Originally Posted by dksob81

I also have a good evaporator core NEW, well slightly used for 1 week, well technically it wasn't used but for 1 day. I charged the system and put die in the system but then after about a day of messing around with trying the get the compressor to kick on I decharged the system but I noticed it was low again and thought I damaged the evap core when I put it together but my leak was coming from the high side shrader valve. Well I put the new evap core in anyways because I had to pay for it because it was a special order and the other one was a different design,the core was the same design plate fin type but the tubes were slightly different one had a loop in it. but was still a perfect fit. The Evap Core will fit any ZJ 95 - 98 and maybe earlier models as well.

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