FJ 62 AC Diagnostics - Help Needed (1 Viewer)

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Hi Folks - I need some AC troubleshooting help. I have searched extensively in the forums, but can't find an answer (at least one that clicks for me), so am hoping that with the info below someone will recognize that I have an obvious problem, or if not, point me in the right direction for further troubleshooting. I am definitely learning the AC stuff as I go, so please feel free to call out any mistakes I made below.

Tools purchased/used, and threads referenced are listed at the end of this post.

So, here goes...

What I Started With

When purchased, the AC was not blowing cold (dash switch light would come on, and compressor was engaging). Local shop added R12. It blew cold for ~4 months until one day while highway driving I started smelling something burning, and noticed the air temperature at the vent decreasing rapidly. I switched off the AC with the dash switch, and pulled over. Upon inspection the compressor had blown oil out of it (all over the engine compartment). I continued my drive with the AC off, until I started hearing a noise from the engine. Upon further inspection the compressor was very difficult to turn (clutch not engaged), so I removed the AC belt in a gas station parking lot and continued my trip (LA to MT and back). It stayed this way until a few weeks ago when I decided to dive in to fix it.

What I Have Done So Far
-Replaced the compressor with a new unit from Coolstream (Denso 471-1433)
-Replaced the receiver/drier with a new unit from Coolstream (Denso 478-0101)
-Added 0.7 oz of mineral oil to the receiver drier, per FMS (also from Coolstreeam #MT3048)
-Removed and cleaned evaporator (should have tested the pressure switch and thermistor, but didn't)
-Pulled vacuum and charged with two 12oz cans of R12 that I bought out of the trunk of a sketchy guy from Craigslist (assuming I am now below spec of 28oz in system)

Current State
-AC Compressor does not engage
-When jumped, AC blows at 44℉ (blower: high, RPM at 2k) and can see bubbles in the sight glass
-Need some help with troubleshooting (below)

Charging
-After installing the compressor and receiver drier, I followed the instructions in post #14 of This Thread along with this youtube video to pull a vacuum, and charge (I'm sure the video content is obvious to some, but being an AC noob it was helpful to me).
-I did everything in the instructions, and couldn't get the compressor engage (pressure was building on the gauges, R12 can tapped, nothing happening)
-I jumped the compressor, and added the two cans of R12. Temp at vent steadily decreased until about 55℉
-Shut everything down, removed compressor jumper.
-Restarted engine, turned fan on, switched AC on. Compressor would not engage.

Troubleshooting: I then began working my way through the troubleshooting section of the FSM, beginning with the "Magnetic clutch does not engage" section on page AC-8

(a) FL (30A CDS) blown - Nothing else on the truck is non-operational. Am I missing something?
(b) Magnetic clutch relay faulty - Does this refer to the Heater Relay?
(c) Magnetic clutch faulty - Checked/Good
(d) A/C Fuse faulty - Checked/Good
(e) A/C Switch faulty - Checked/Good
(f) Thermistor faulty - Am I correct that I can't check without recovering refrigerant and pulling evaporator?

(g) A/C Amplifier faulty -
Testing conditions: IGN on, temp control lever Max Cool, Blower switch Hi
Continuity
6-Ground: FAIL
7-6: Good
8-9: Good
9-Ground: FAIL
Voltage
2-6: Good
3-6: Good
A-6: FAIL

Based on this my guesses are that I have a bad ground on the WB (white w/ black) ground wire OR the thermistor is bad. Thoughts?

IMG_1435.jpg


Amplifier passes a visual check (no burned out pins)
IMG_1426.jpg



(h) Pressure switch faulty -
I am not totally clear on how/where to test this, but here is what I tried.
-Based on the wiring diagram on page AC-4, I tested continuity between the Y (yellow) and YG (yellow w/ green) wires at the amplifier harness plug (pins 2 and 3 in the pic above). Here is a video of the results. Readings went from 0 to ~12.6 in a few seconds.

Also, here are the pressures at the gauges with the following testing conditions: Compressor jumped, Blower at high, Temp control at cool, AC switch on.
Low: 18psi (spec is 21-28psi)
High: 235psi (spec is 206-213)

Based on this I am not sure if my pressure switch is bad, or if I am low on refrigerant (causing the non-spec reading).

IMG_1433.jpg


(i) Wiring or ground faulty - Possible. See above "amplifier faulty" section
(j) Refrigerant empty - Not empty, but not full either

IMG_1431.jpg



Tools Used/Purchased
-Gauges (borrowed)
-Vacuum pump - Amazon $58.99
-Higher Quality Oil for Vacuum Pump (per Amazon comments) - Amazon $16
-R12 Can Tap - Amazon $8.49
-High side R12 Adaptor #MT0961 - Coolstream $14.19 (also available from Autozone for $9.79) *this is needed to connect gauges to the high side compressor port. Found in this thread (thanks @1972FJ55)

For others, these were threads that I found helpful:
-Yet another AC Thread by @georgebj60 - Great pictures
-Heater and AC System Re-Foam by @red66toy - Excellent writeup for removing, cleaning, and re-foaming evaporator case
-FJ62 New AC Compressor Part Number & R134 Fittings by @PNWFJ80 - If retrofitting to r134, this is the list
-Stay with R12 or convert to R134a - Great summary of pros/cons
-FJ62 A/C overhaul with Denso 10P15C compressor rebuild by @Spook50

Thanks everyone,

Dave

IMG_1435.jpg
 
Last edited:
Joined
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If you've got pins on the connector that should have continuity to ground but don't why not just run a temp wire to ground see what happens. Then chase down the actual ground if it's bad.
 

red66toy

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Why does that pin in the center of your amp board pic look like the soldering came off? Is that actually how it supposed to be? I cant remember what the back of my board looked like but that doesn't look right.
Definitely check your grounds like @Prairie Swamp suggested
 
Joined
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If the 'pressure switch' that is not closing is just the low pressure cutout switch, I would jump it for now. That switch just exists to protect the compressor against running without oil or refrigerant pressure.

If you installed 2 cans of R12, you have plenty of refrigerant to make the system work as it should (plus/minus a little bit). 44F is an excellent center-vent temp, and what I got on mine after charging. 'Some bubbles in the sight glass are acceptable, especially right before/after the compressor cycles (normal cycling). Your low and high side pressures are excellent (albeit the low side looks almost too low for my tastes).

If shorting the pressure switch allows the system to operate, I would do that for a few days and see how the system performs, and then go back to debugging. Can you find a used A/C amplifier to buy and test, to see if it checks out just like yours?
 
Joined
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Thanks guys.

Great call on simply jumping a few things. I tested the ground (WB wire), and it had continuity. Per @SteveH I moved on to jumping the low pressure cutout at the amplifier plug, and that did the trick. Compressor kicked right on. Thank you for chiming in that my pressures looked ok, and that it is ok to see bubbles.

I took it for a test drive and was reading 34.8℉ at the vent.

So, to replace the low pressure cutout my understanding is that I have to recover the refrigerant (or blow it off), remove the evaporator, replace the switch, reconnect everything and then pull vacuum and recharge. Is this correct? I would rather not burn any holes in the ozone layer with the R12 (or have to call the sketchy guy for more cans), so am working on finding someone with an R12 recovery bottle that will give me a hand.

Regarding the amp board, it looks like the pin that is missing the solder is from the relay looking component (Denso 056700-8140), and I traced in red the rough footprint from the back. A cursory google search did not come up with anything for that relay. But, I am wondering if that pin is used at all since it is not positioned on a circuit (dark green vs light green). At any rate, Specter Off Road lists used AC Amps for $460 (053-70M-U), so that is definitely not happening. I might swing by there and look at one to compare if I find some time. I'll report back with a comparison if so.

IMG_1438.jpg
IMG_1441.jpg
 
Joined
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Great job on getting the system to run, and generate such lovely low temps from the vents. Don't add any Freon at this point!

Regarding the amp board, it looks like the pin that is missing the solder is from the relay looking component (Denso 056700-8140), and I traced in red the rough footprint from the back.


There isn't even a copper trace on the board for that un-soldered relay pin, so that's not your problem. You are correct about having to vent/recover the R-12 if you replace the cutout switch, so I would delay doing that as long as possible (perhaps forever - just leave the jumper there for now). I'm sure you can find a used A/C amplifier on Mud for less than SOR's price, and that might be a good pursuit.

What else is still jumped or non-stock at this point?
 
Joined
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Thanks Steve. It is super helpful having my thought process confirmed (vent/recover, etc).

Makes sense about the board. I found one on ebay and it shows the same non-soldered pin in the listing pics, so looks like it is stock.

But, in thinking through it, with the pressure switched jumped do I have a bad amplifier? I am thinking that my amplifier might be ok, but the pressure switch has failed. Either way, I just grabbed the ebay amplifier for $50 and will plug it in to see if that fixes it (seems good to have a spare...). Pressure switch from Oreillys is ~$18.

Screen Shot 2018-08-20 at 12.15.32 AM.png
 
Joined
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At this point, you'll learn more when you install the eBay AC amplifier, correct? If it's working correctly, I presume your current pressure switch shows continuity right now, since you have Freon in the system. If it does not, then it's bad.
 
Joined
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Yes, the continuity goes from 0 to ~13 ohms over the course of about three seconds (here is a video). Not sure if that is normal...

I'll pop the used amplifier in when I get home from a work trip and report back with results.
 

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