Couple quick questions

Ok, two slightly varied topics here, one I'm looking for info on and the other more of a "casual interest" thing.

First off, the info request. I'm getting water dripping from the heater box only when the A/C is on (and the box itself is sweating pretty good after an hour's drive. A/C drain does appear to be working (truck drips nicely when I park it), though I may check it anyway.

A little search-fu turned up reports of evaporator icing in the 97+ models, seemingly caused by a failed A/C low-pressure switch. This got me to wondering the following:

1. Are the earlier models also prone to this issue? I have a '92 that's been converted to R134 (blows nice and cold). I don't think I have a drop-off in air flow through the vents, but can check on the drive home tonight.

2. The low-pressure switch on the 97+ is supposed to be replaceable without depressurizing the A/C system - is this also true of the older models as well?

3. Is there a way to test the switch, or is it so cheap that slapping a new one on is the path of least resistance?

4. What would I look for in a new switch? Does it matter whether I'm running R-12 or R-134?


And now, on to my matter of "casual interest". I've been noticing the console lights dimming and cluster voltmeter dropping down from the "1" in "14" almost to the white mark above the lower red zone when sitting at idle with the headlights on (only happens if the headlamps themselves are lit). Once I throttle up to move, it goes right back up. Two nights ago I experimented in the driveway with the headlights aimed against a wall, and could detect no change in the brightness of the headlights themselves as the voltmeter dipped and came backup (from revving engine). Don't notice any change in engine pitch/smoothness at idle when the voltmeter phenomenon occurs.

Battery is a 2-yr-old Yellow top. Engine off voltage is 12.5, drops only to about 11 when cranking, jumps right up to 14.3 or 14.4 once engine running at idle (Stock 90A alternator). Battery cables were replaced over the weekend with a 4AWG set from 5-90 (block-firewall cable still in toolbox until I can figure out how to get the nut holding the block end of the braid loose) including ANL fuse retrofit.

This started happening only recently, and before the cable replacement. I've heard that this is not unusual for XJs, but as it's a departure from what I consider to be "normal" for the truck, it's got me scratching my head.

Thoughts?

I wouldn't be too concerned over it. The XJ voltmeter reads at the end of all the loads.

Not sure if you have the temperature sensor under the battery, but you might consider testing that.

You should see an improvement once the unibody ground is upgraded.

Good luck.

joe_peters said:

I wouldn't be too concerned over it. The XJ voltmeter reads at the end of all the loads.

Click to expand...

I remember hearing that, and since I didn't notice a change in the headlight brightness itself, I wasn't too concerned anyway (though the dimming of the cluster backlighting can be a bit annoying). I may give some thought to building a relay harness for the headlights, though - it's the original switch, as far as I can remember, so taking the load of the headlights off it might not be a bad idea...

joe_peters said:

Not sure if you have the temperature sensor under the battery, but you might consider testing that.

Click to expand...

No sensor under the battery. Musta been an OBD-II thing.

joe_peters said:

You should see an improvement once the unibody ground is upgraded.

Good luck.

Click to expand...

Hm. I have six of the seven cables (due to ANL retrofit) currently run:

Battery pos to starter
Battery pos to PDC
Alternator output to ANL fuse
ANL fuse to Battery pos
Battery neg to fender well
Battery neg to block

Only block to firewall remains original at present (nut wouldn't come loose, need to work on it more). Think if I cleaned it up I could get away with stacking the new cable on top of the original one? plenty of stud left to put another lug and nut on it.

Thoughts on the A/C?

I've added a ground cable from the dipstick tube stud over to the passenger inner fender stud near the upper shock mount to supplement the head to firewall one. The stud is metric by the way, 8mm X 1.25.

I got curious about your a/c question. I assume you are speculating that your evaporator is icing as evidenced by condensation on the exterior of the air box while the a/c is running?

It was cloudy here this morning for the first time in weeks (otherwise I probably wouldn't have gone out to play with this) and I wanted to do some IR thermometer testing anyway. About 94* ambient/56% humidity. Xj is a '93 converted to 134a. I started and let it idle with a/c switching between max and norm and with passenger door open and closed. In dash vent test thermometer stayed at 50* while idling. I never got any condensation that I could feel anywhere on or about any of the HVAC stuff under the dash. Condensate "poured" out under the truck but was dripping out of the frame rail which I assume means there is a problem with the drip tube.

If you had asked me what causes icing, I would have said various factors related to a low refrigerant charge. There are certainly guys on the forum that can give you a definitive answer.

I am reasonably certain that you can change out the low pressure switch without depressurizing the system and that it makes no difference whether R12 or 134. For example, I noticed several weeks ago that teamcherokee.com has a factory original switch for '84 to '96 for around $64. I'm pretty sure you can get aftermarket ones a lot cheaper but haven't checked.

The key, though, would seem to be that your a/c blows "nice and cold" and do you really want to mess with it. A unit with a frozen evaporator coil will not blow cold air for any length of time. Ice will melt and drip and the process will start all over again. I'm not sure that there is any greater likelihood of getting condensation on the exterior of the box with icing than with normal operation of the a/c.

After all this, I don't have an answer to your interior condensation problem but a guess would be that your drip tube is partially dislodged, allowing some condensate to drain but also allowing some cold air to bathe the exterior of the box and cause the condensation. Anyone with a different thought?

Obviously you do want to fix this or you will end up with wet carpet and maybe rusted floors.

Let us know what you find out.

You have a point in that if it's working, messing with it's probably not too wise. Then again, having been through the rotted floor routine I'm not eager to repeat it.

I'll have try to locate the inside part of the condensate drain this weekend and get an eyeball on it. I did have the entire dashboard out about 2 years ago to have the cowl-duct seal replaced (source of a water leak that ate my floorboard).