A/C cooling stops after 30-60 mins (1 Viewer)

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Hflcruz

SILVER Star
Joined
Feb 6, 2020
Threads
2
Messages
53
Location
Houston
Dear Fzj80/Fj80 Experts,

My 1997 has an AC problem.

Every morning it starts cooling perfectly.

Then after 30, or 45 min sometimes a bit more it all of a sudden stops cooling.

I've used a code reader to read real time engine temp and it nerver goes above 195- 197F . Read that the AC cut off relay is activated at 220F.

The AC clutch engages perfectly as I see its effect on engine RPM if I turn the AC on or off.

So far I do not understand where is the issue. Could it be a Frozen Evap? Or AC amplifier or AC system amplifier?

I read the FSM trouble shooting. Checked the little visor next to the battery. As per instructions. When AC is turned off threre should be bubbles and they should then dissappear. When the AC stops working. I trun the AC off and there is no bubbles.

Any suggestions?

Thanks!

Hernan
 
Refrigerant may need servicing. The system loses a couple percent every year.
 
Refrigerant may need servicing. The system loses a couple percent every year.
^^^^

This would be where to start. A low refrigerant charge can cause short cycling and a frozen evaporator.

A faulty thermistor on the evaporator...the same thing.
 
When AC is turned off threre should be bubbles and they should then dissappear. When the AC stops working. I trun the AC off and there is no bubbles.
When the AC is turned ON, you should briefly see bubbles in the sight glass and it should run clear after a bit of time.
Looking at the sight glass with the system off tells you nothing.
 
@jonheld in my post I meant to say that I looked at the sight glass just after shutting down thr AC function. - as per FSM checks. No 6. Below.

SmartSelect_20210424-161659_Chrome.jpg
 
Stop guessing and put gauges on the system. Once you are certain that the refrigerant pressures are correct, you can move on to other items. Looking at the sight glass is only the very first step.

Even looking at the sight glass can be a total waste of your time and perhaps lead you down a rabbit hole you don't need to go down.

I have cautioned about that for years. I don't know why the FSM even has that information in it. Its a hold over from R12 days when that exercise actually meant something.

Or....if you are way the hell out in BFE, have no gauges and desperately need to charge the system, it is a rudimentary way (and I'm being generous here) to determine when to stop adding refrigerant.

R134a is MUCH more prone to 'flash gassing' coming out of the drier. That by itself will cause 'bubbles' to appear. If you have too much oil in the system....that will appear as 'bubbles' though its actually streaking.

Sheesh....even in the FSM it states if NO bubbles are present it could be because the charge is:

None
Sufficient
Too Much.

Well which one is it? And how would a novice hope to know. USELESS!

Then the FSM touts that if the sight glass stays clear after shutdown that you have Too Much refrigerant. Simply not true depending upon the ambient temperature. Its going to take a bit for the system to begin to equalize.

So as you correctly suggest: Put a set of gauges on it.

We live in a first world country and have the technology, use it.
 
let's move inot to other items.

As I stopped at the first general shop I could find. Same day I received the truck

Just to check pressures and perhaps the system needed rrcharge. The mechanic was puzzled. He said pressures that were fine.

I am going to take it to an AC specialist
However, not a FZJ80 AC specialist (hence the reason for this post).

Potentially I will purchase a set of gauges and try to gain more information.
 
What are the standar preasure ranges should see in low and high side of the compressor. Or else in the system.

Where can I access this information?

I can get gauges but then, is the system like for like in terms of pressures with any other truck?

I seen a few youtube videos on, however non specific to FJ80.

Appologies in advance, I have never trouble shoot AC before.

I only have youtube, Google, FSM, and the Electrical wiring diagram which is by far one of the most useful resources on trouble shooting.

Ahhh... I also have very very limited time. I.e. 2-3 hours per week. But I am not in a rush either.
 
I can get gauges but then, is the system like for like in terms of pressures with any other truck?
It's not related to cars, it's temperature pressure relationship of each kind of refrigerant, so yeah, pressure for r134a it's for all cars the same.

You are lucky to have r134a test pressure ports on your compressor, it's getting pretty easy to check with quick-connector
 
The correct (or acceptable window) of pressure (high and low sides) will depend on the ambient temperature at the time you check the system.

Regardless of whether the shop said the pressures were 'OK', they need to be checked again so we have a known starting point.

IF indeed the pressures are alright then we can move on to troubleshooting the rest of the system. There are multiple reasons why the system will cool for awhile then stop.

The most likely are:

  • Evaporator is freezing up
  • TXV is freezing up
  • Thermistor is faulty (causing evap to freeze up)
  • Relay is failing intermittently
  • Moisture in the system....freezes and causes blockage
 
When the shop checked the pressures, was it cooling? What you're describing sounds like the expansion valve. With the gauges attached when it stops cooling, usually the low-side reading will go to zero or into vacuum. In order to replicate this when a customer would come in with the complaint that their vehicle would stop cooling after awhile, we would put gauges on it and let it idle until it stopped cooling and see what the gauges read. Most of the time it was the expansion valve.
 
When the shop checked the pressures, was it cooling? What you're describing sounds like the expansion valve. With the gauges attached when it stops cooling, usually the low-side reading will go to zero or into vacuum. In order to replicate this when a customer would come in with the complaint that their vehicle would stop cooling after awhile, we would put gauges on it and let it idle until it stopped cooling and see what the gauges read. Most of the time it was the expansion valve.

Yep,

If a shop didn't run the system long enough for it to stop cooling, then they did the customer a disservice.

Typically a 'Stopped Cooling' issue means something froze up. (Evaporator or TXV Thermal Expansion Valve). So the only thing left to do at that point is determine WHY.

Is is a low refrigerant charge causing the evaporator to freeze up?
Is there moisture in the system allowing the TXV to freeze up inside?
Is the TXV itself stuck?
Is the Thermistor on the Evaporator faulty....allowing the evaporator to freeze up?
Is the Evaporator all clogged up with debris not allowing enough return air across it (can cause freezing)?
 
maybe you ought to bring it to Javier - I understand he's a cruiser guru in Houston

I can find out contact info, let me know
 
Just a point from your first post. You said

"The AC clutch engages perfectly as I see its effect on engine RPM if I turn the AC on or off. "

This is not a way to accurately know that the clutch is still locked up and turning the compressor. The RPM is controlled by a "valve" up on the throttle body. It can change RPMs regardless of A/C clutch state. When it stops cooling, you must get out and take a look at the front of the compressor to see if the entire clutch assembly is all locked up and turning.

To state what the others are saying in a different way, the only way to know if the system has the correct amount of freon in it is to to remove it all with a vacumm pump, then measure it accurately when recharging it. Guages are a great tool, but they can not measure the exact amount of gas in the system. Because of this, it costs a good amount of money for a shop to hook up their fancy machine to your truck , remove all the freon, and THEN tell you if it has the correct amount of freon in it. A $teep diagnostic price, but necessary.
 
Dear Fzj80/Fj80 Experts,

My 1997 has an AC problem.

Every morning it starts cooling perfectly.

Then after 30, or 45 min sometimes a bit more it all of a sudden stops cooling.

I've used a code reader to read real time engine temp and it nerver goes above 195- 197F . Read that the AC cut off relay is activated at 220F.

The AC clutch engages perfectly as I see its effect on engine RPM if I turn the AC on or off.

So far I do not understand where is the issue. Could it be a Frozen Evap? Or AC amplifier or AC system amplifier?

I read the FSM trouble shooting. Checked the little visor next to the battery. As per instructions. When AC is turned off threre should be bubbles and they should then dissappear. When the AC stops working. I trun the AC off and there is no bubbles.

Any suggestions?

Thanks!

Hernan
Thanks for this...I just got my AC serviced and it's been blowing cooler than before (seemed like it wouldn't cool when the ambient temp was above 90F). Then driving back from Vegas the AC just stopped as I was heading up the grade from State line to LA (ambient temp was 105F). I looked at the temp gauge and it was close to the red (never seen that before). As soon as I got to the plateau, the temp dropped to 95F, and the temp gauge dropped back to the mid range and the AC turned back on...Whew!! I was worried there was a leak or something worse.
 
Thanks for this...I just got my AC serviced and it's been blowing cooler than before (seemed like it wouldn't cool when the ambient temp was above 90F). Then driving back from Vegas the AC just stopped as I was heading up the grade from State line to LA (ambient temp was 105F). I looked at the temp gauge and it was close to the red (never seen that before). As soon as I got to the plateau, the temp dropped to 95F, and the temp gauge dropped back to the mid range and the AC turned back on...Whew!! I was worried there was a leak or something worse.
You should probably look into your cooling systemt (radiator etc.) as it sounds like you hit temps above the AC cuttoff. Not sure how much weight you were carrying or how steep the grade was but a well functioning cooling system should be able to handle a grade at that ambient temp. I would start with a obd2 bluetooth scanner or scanguage type system to get accurate engine temps while driving around to get a sense of your systems efficiency (or lack of efficiency).
 
Thanks for this...I just got my AC serviced and it's been blowing cooler than before (seemed like it wouldn't cool when the ambient temp was above 90F). Then driving back from Vegas the AC just stopped as I was heading up the grade from State line to LA (ambient temp was 105F). I looked at the temp gauge and it was close to the red (never seen that before). As soon as I got to the plateau, the temp dropped to 95F, and the temp gauge dropped back to the mid range and the AC turned back on...Whew!! I was worried there was a leak or something worse.

Most likely what you experienced was the Coolant Temperature Cut Out switch doing its job. When coolant temps exceed 226-227°F the Cut Out switch will disable the A/C compressor until the coolant temp recedes to between 216-220°F. This is by design to help avoid further overheating of the engine.

Unfortunately, it is not a well known feature *outside of the MUD forum* and can be a bit disconcerting the first time you experience it. Not only do you notice your vehicle's temp gauge climbing....but now your A/C has cut out to add to the worry.

In a way its a useful forewarning of impending engine overheat. Because the factory temp gauge has a HUGE 'dead spot' in it....where it doesn't move at all until you are just about in the danger zone.

So IF you have your A/C on and it does that again, check your engine coolant temp. If too high.... take measures to improve your cooling system .
 
You should probably look into your cooling systemt (radiator etc.) as it sounds like you hit temps above the AC cuttoff. Not sure how much weight you were carrying or how steep the grade was but a well functioning cooling system should be able to handle a grade at that ambient temp. I would start with a obd2 bluetooth scanner or scanguage type system to get accurate engine temps while driving around to get a sense of your systems efficiency (or lack of efficiency).
Agreed...the grade wasn't crazy steep and it was just me, my wife and daughter with about 150 lbs of luggage lol ! (Daughter was in a dance competition)- was just looking into an OBD2 bluetooth scanner - any suggestions? I'm going to have the radiator flushed when I take it in for service then see what's what.
 

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