Installed Brown Dog Motor Mounts... now No AC??

Ok... so I installed the Brown Dog Motor Mounts this weekend on my '01 XJ. Install went great and easily. I re-used the OE thru bolts and after snugging them up a bit too tight and getting a lot of vibrations, I emailed BD and was told to try and back the nuts off ~ 1/2 turn... did that and just tried it and it would appear the vibrations are gone. More on that after putting a more miles on her.

OK... now on to my question. I tried running my AC after lunch when leaving the gym today... and nothing, nada, hot air. The AC compressor wouldn't even cycle on at all. I had just ran the AC last week and it ran fantastic. I actually had the 'dryer' or 'accumulator' replaced this past winter when my 0331 cylinder head was replaced. The shop loaded up my AC system, held pressure and worked fine.

So, when installing the motor mounts the only thing I unhooked was the switch/wire f/one of the AC lines. Not sure if it was the Hi or Low pressure side. Here is a pic



The only other wire that got moved around a bit was below the AC Compressor and I didn't have to unplug it or anything and it appears to be in good condition... pic below



That wire runs up and to the front of the compressor and is attached to here...



Here is what was replaced earlier during the head swap as mentioned previously



I am getting nothing when I turn my AC control to Max, Defrost, Mix or any other spot and the compressor doesn't cycle on/off at all.

Does anyone have any ideas what could have caused this all the sudden? Is there a way to 'jump start' the AC compressor to see if there is a bad switch, fuse, wire, something?? Any ideas would be appreciated.

Here's an obligatory pic of the Passenger Side Brown Dog MM. They are very well made and like everyone here, I HIGHLY recommend them.



Thanks all

The first pic is of the high-pressure switch, mounted on the compressor discharge line (hence the test port on the same line - low pressure is mounted near the accumulator). The second appears to be the compressor clutch lead.

If either is not working or has a poor connection, the A/C system won't operate (someone please correct me if I'm wrong - I get the feeling that it might still operate under some conditions or failure situations).

In any case, triple-check those connections. Inspect pins on both the male and female sides, and make sure they're fully seated. They appear to be, but I'd need to look at mine (the high-pressure switch plug appears to have some of the red locking tab missing, so it's hard to tell if it's fully seated).

Thanks f the reply. I double checked the HP connection a couple times and the red safety 'latch' is in tact & snapped in place. It could however have a short ... I'll double check that.

Should there be a POS & NEG on any of these wires when the AC is set on?

Thx

The wire going around the front of the a/c compressor is the clutch coil power wire. I would turn on the a/c and see if it has power if it does and clutch isn't spinning them it's the clutch coil. If not trace the wire back until you find where the power stops, most likely at one of the pressure switches.

You can jump the low pressure switch (at the accumulator) with a piece of wire or paper clip. That will activate the clutch on the compressor and keep it engaged so long as the wire is inserted in the connector. If that works then the switch is probably bad and can be replaced without losing refrigerant.

As a follow-up... can the High Pressure and/or Low Pressure AC Switch be replaced w/out discharging the AC System? Since I've never done that I'm not sure if the switches are an integral part of keeping the system charged or not.

Redsnake said:

As a follow-up... can the High Pressure and/or Low Pressure AC Switch be replaced w/out discharging the AC System? Since I've never done that I'm not sure if the switches are an integral part of keeping the system charged or not.

Click to expand...

Yes, the switches are removable (they unscrew) and have a Schrader valve that prevents refrigerant loss. If it turns out that the switch is bad I'd buy one from Jeep. There was a FSB or recall on the switches (not sure of the years).

AC work can get complicated and is best left for the pros but if you don't mind throwing a few bucks at the problem you could start by getting a can of refrigerant that comes w/leak detector (no stop leak) and a gauge and is reusable. I use that to top mine off occasionally due to a leaking Schrader valve on the low side. Get the engine warm, hook up the gauge/can to the low pressure side and with the AC on Max try adding the refrigerant. If the compressor won't cycle try disconnecting the switch and jumping it.

The compressor should start running. Take note of the reading on the gauge, if my memory is right the low pressure should be between 30-40. If the pressure is low add refrigerant till the pressure is up, but don't over charge it. Hook up the low pressure switch and see if the compressor cycles. It should cycle no more than 10 times per minute.

The high pressure switch is there to prevent damage to the compressor if the pressure gets too high.

If you get cool air but it stops working after a few days/weeks you can buy a special UV light to check your connections for the dye. There's a good chance that, like many of us, the crappy evaporator is leaking...spend a grand to fix it, tear the dash out or roll down the windows. Good luck.

weebur thanks for the info.

I'm pretty confident is something easy as I had some AC work done just a few months back when I had to get a new 0331 cylinder head installed. The AC worked just fine last week before I did the MM install in which I unplugged the High Pressure switch to gain access and not worry about possibly busting one of those switches or wires.

I ran my voltage meter and couldn't get any voltage to the compressor w/the negative touching the battery and positive touching the wire connection as the front of the compressor (could be I was WAY off in my thinking here) just to see if I was getting anything. I disconnected the Hi Pressure switch and got 12V to the 'green' wire but no other wires (this was why the switch was unplugged) so not sure about that.

I may end up running it by the shop who did the work on my rig this past winter and see if the can do a quick diagnosis and fix. Trouble is they are a really good shop (something hard to find if you ask me...) and they're always busy. May have to drop my rig off for a few days and that's not something I want to do right now.

Followup...

I pulled the low-pressure switch and jumped it w a wire... the AC Compressor kicked on but no cool air. Hooked up my AC check gauges and w the AC Compressor running I had zero pressure readings on both Low & High sides.

Not sure how I could've lost all the coolant in a couple days, but is that possible?

I may try and add some 'freon' to the low side & see how long it lasts & then check f dye.

Any suggestions or does this sound like an appropriate next step before taking to the shop?

Thx

Redsnake said:

Followup...

I pulled the low-pressure switch and jumped it w a wire... the AC Compressor kicked on but no cool air. Hooked up my AC check gauges and w the AC Compressor running I had zero pressure readings on both Low & High sides.

Not sure how I could've lost all the coolant in a couple days, but is that possible?

I may try and add some 'freon' to the low side & see how long it lasts & then check f dye.

Any suggestions or does this sound like an appropriate next step before taking to the shop?

Thx

Click to expand...

It sounds like you had a catastrophic leak/failure. Small leaks at the O-rings will sometimes stop when the pressure is lowered to a point where the leak will stop. Having absolutely no pressure in the system is not a good thing.

It can't hurt to add some refrigerant w/leak detector at this point and then check for leaks. The compressor will need to be working/cycling to circulate the dye. I have used the penlight UV lights to check for the dye, but they're weak and you'll need to check it at night, or buy a good/powerful one, but they're expensive. Check your line connections for leakage, even without the dye in the system you'll see an oily residue at the connections where the O-rings are located. All of the connections should be bone dry.

There were problems with leakage at the high pressure connection line at the compressor leaking (not sure of the years involved). The fix was to install a washer under the bolt connection, so check there also.

If you can't find any evidence of leaks at the usual places make sure you check the HVAC box drain tube for the dye. Dye there means your evaporator is leaking as it will mix with the normal water that comes from ice melting on the evaporator coils that drains out to the ground.

If nothing else you'll be armed with some information before you take it to a shop. Keep us posted on your progress as there will be tons of questions on AC problems with summer just around the corner.

Thanks f the info...

Just loaded one small can of 134a w UV to my system. I had jumped the Low Pressure switch so the compressor was running. The pressure gauge on my refil hose showed ~34psi and started blowing cold air out the vents. No noticeable leaks but time should tell & hopefully w the UV due ill be able to find the leak.

I plugged the LP Switch back in & the Compressor shut off & wouldn't come back on even though I was getting cold air & ~34psi. I'm wondering if the switch is bad now? Also, is it bad to have the LP switch jumped 100% of the time & keep the compressor running all the time?

I'll follow up as soon as I loose the cold & see if I can find the leak.

Thx

Redsnake said:

Also, is it bad to have the LP switch jumped 100% of the time & keep the compressor running all the time?

Click to expand...

Yes!

The compressor on my '93 has never cycled, at least in the seven years I've had it. (The LP switch is not jumped.) I have wondered why and what bad things are going to eventually happen because of this?

My understanding was that if the AC had a proper charge then the compressor would never cycle off, but I don't know for sure.... Likely there are several factors that dictate the compressor cycling.

With the AC on full blast on a hot day with the XJ sitting, the compressor do not cycle. However, if I were to turn the fan speed lower or go for a drive which mean the engine would run at a higher speed the compressor would cycle.

I do not know much about AC but I was told the low pressure switch help to prevent pre-mature compressor failure. The reason being, oil and the R134A are mixed and circulates in the entire system. A loss of the R134 means a loss of oil also.

Just a follow up...

Had my XJ in at the mechanic yesterday and he ran some tests and turns out my leak is indeed coming f/the evaporator. He pulled a long vacuum, refilled and tested. His leak 'sniffer' went nuts when up next to the evaporator. Now to see how long she holds a full charge and perhaps see if we can get by running a product he said he's had really good luck with in a 'sealer' type product. That's assuming the leak is very minor and not all gone in the next couple of days. Cost to replace the evaporator and refill and test is ~ $950 (figuring 8 hrs labor)... and cost for the 'sealer' would be ~ $350 w/a lifetime warranty on the product. We shall see.

Any suggestions f/the peanut gallery? I know I could run some R134a w/Sealer in it myself, but he said that the product they use they have to pull a good vacuum and dry out the entire system as this apparently reacts w/water to create the seal. I'd hate to spend $350+ on this only to have it not work then shell out another $950 to pull the dash and replace the evaporator. This route would cost me a bit more as I'd make sure he replaced the heater core while the dash was out just to be safe due to my rig having 126K+ miles...

You can do the evaporator yourself if you don't mind being under there for like 8 hours from what I've read. Not looking forward to it myself but there are a lot of things I will wrench myself to save $1k, personally.

If you want to play it safe, buy an evaporator and have him evac the system, then do the replacement yourself and have him pull a vacuum and charge it.