AC doesn't run, and efan doesn't run, unless they are jumpered

[bigalpha]

My AC doesn't work and the efan doesn't work.

When the AC is selected in the cabin, the compressor didn't start and the efan doesn't turn on.

I can jump the relay for the AC and the compressor will turn on. It looks like there's refrigerant in the system, because I think I can see some cycling through the little window, but the air never gets cold and the lines in the engine bay also don't get cold. There is no continuity at the connector to the low pressure switch.

When I jump the relay for the efan, it will turn on, but does not turn on otherwise. It stays off even if the coolant sensor (at the tstat) is unplugged.

I jumped the low pressure switch and the e fan didn't come on, but I'm unsure if that's diagnostic or not.

The only other thing is the Jeep isn't running at 14+ volts; at the battery, I measure about 13.8V. unsure if that matters, either.

I know that low refrigerant won't allow the compressor to kick on, but is there another place to check that, if failed, could mess with the AC and the fan?

 

[lawsoncl]

The obvious answer is that you no longer have enough freon and pressure in the system to engage the low pressure switch.

 

[lawsoncl]

A 1992 takes R12, so unless it's already been converted you can't just recharge it.

 

[bigalpha]

The obvious answer is that you no longer have enough freon and pressure in the system to engage the low pressure switch.

Sure, that makes sense and kind of what I figured. Does that explain why the fan doesn't work right?

 

[bigalpha]

A 1992 takes R12, so unless it's already been converted you can't just recharge it.

Yeah, it needs to be evacuated first, right?

 

[Saudade]

Sure, that makes sense and kind of what I figured. Does that explain why the fan doesn't work right?

Yes. The efan engages with the compressor, or when the coolant gets too hot.

 

[RCP Phx]

Yeah, it needs to be evacuated first, right?

You need to do a parts conversion to be able to accept R-134.

 

[Saudade]

Yeah, it needs to be evacuated first, right?

It's bit more complicated. If you're low on freon, you have a leak somewhere. You need to locate and repair the leak.

If you have any freon still left in the system, the law says you can not vent it into the atmosphere as R-12 is an ozone depleting gas. You can go to a local AC shop have have it reclaimed.

Real R-12 is expensive. 1 12oz can runs around $30-$40 on ebay plus shipping. Plus you have to be certified under EPA Sect 609, or certify that it will be used by a certified technician.

There's a lot of fake and substitute R-12 out there. Much of it contains propane and/or other flammable substances.

You can convert like Lawson suggests to r-134a. R-134a is being phased out but still widely available (and still relatively cheap). You'll still need to reclaim the R-12, flush out the old Mineral oil, replace the drier, etc. There are quite a few threads on this.

 

[lawsoncl]

Put more plainly, this rabbits hole is likely deeper than you think.

You'll likely pay a shop more than the bluebook value to repair/convert the a/c. Figure at least $1000 a they'll insist on replacing the compressor, drier, etc. There are some DIY conversion kits out there, but you'll need to find that leak and replace parts, and have access to a few specialty tools to do it right like a gauge set and a vacuum pump (both can be borrowed/rented at Autozone).

 

[bigalpha]

Yes. The efan engages with the compressor, or when the coolant gets too hot.

The efan currently does not come on at all, even if it's above temp. It does work if I jump the relay, though.

 

[lawsoncl]

The efan currently does not come on at all, even if it's above temp. It does work if I jump the relay, though.

Test the temp sensor, and inspect the wiring to it. The sensor at the back corner of the head is for the dash guage, not the computer, btw. Unplugging it makes the engine computer think its cold, not hot.

From the 1993 XJ FSM

COOLANT TEMP SENSOR & MANIFOLD AIR TEMP SENSOR RESISTANCE TABLE
Temperature *F(*C) Minimum Ohms Maximum Ohms
-40 (-40) .............. 291,490 .......... 381,710
-4 (-20) ............... 85,850 ........... 108,390
14 (-10) ............... 49,250 ............ 61,430
32 (0) ................. 29,330 ............ 35,990
50 (10) ................ 17,990 ............ 21,810
68 (20) ................ 11,370 ............ 13,610
77 (25) ................. 9120 ............. 10,880
86 (30) ................. 7370 ............... 8750
104 (40) ................ 4900 ............... 5750
122 (50) ................ 3330 ............... 3880
140 (60) ................ 2310 ............... 2670
158 (70) ................ 1630 ............... 1870
176 (80) ................ 1170 ............... 1340
194 (90) ................. 860 ................ 970
212 (100) ................ 640 ................ 720
230 (110) ................ 480 ................ 540
248 (120) ................ 370 ................ 410

 

[Rob Mayercik]

Put more plainly, this rabbits hole is likely deeper than you think.

You'll likely pay a shop more than the bluebook value to repair/convert the a/c. Figure at least $1000 a they'll insist on replacing the compressor, drier, etc. There are some DIY conversion kits out there, but you'll need to find that leak and replace parts, and have access to a few specialty tools to do it right like a gauge set and a vacuum pump (both can be borrowed/rented at Autozone).

When I had my 92 converted to R134 about 15 years ago, wasn't replaced. It's the same compressor that was in the truck when I bought it just shy of 24 years ago, and it's run just as happily on R134 as it did on the original R12 before the first condenser failed and vented the system out. Far as I can tell, it blows as cold with R134 as it ever did with R12.

Maybe a "native" R134 compressor is different from one designed for R12, but in the 15+ years I've run R134, I've not had any reason to doubt what I feel coming out of the vents...

 

[IslanderOffRoad]

Sure, that makes sense and kind of what I figured. Does that explain why the fan doesn't work right?

Pull the electrical connector on the compressor. Then turn the ac on in the cabin. The fan should kick on. I used to do that for manual control of the fan on my 94

 

[lawsoncl]

I jumped the low pressure switch and the e fan didn't come on, but I'm unsure if that's diagnostic or not.

If you jumpered the low pressure switch to trick it to run despite low freon, and turned the a/c on from inside, I would expect the e-fan to run. You'll need to look at the wiring schematic and use a meter to determine if the relay is bad or if the computer isn't calling for the fan to run.

 

[bigalpha]

If you jumpered the low pressure switch to trick it to run despite low freon, and turned the a/c on from inside, I would expect the e-fan to run. You'll need to look at the wiring schematic and use a meter to determine if the relay is bad or if the computer isn't calling for the fan to run.

I swapped the relay with another known working one (starter) and no change to the behavior.

I'm really stumped about the efan. It doesn't even come on when I unplug the temp sensor in the thermostat housing.

 

[bigalpha]

Pull the electrical connector on the compressor. Then turn the ac on in the cabin. The fan should kick on. I used to do that for manual control of the fan on my 94

That's the one-wire plug that is right above the accumulator/drier, right?

If I disco this and the fan doesn't come on with the AC selected in the cabin, what does that mean?