LX450 AC urgent (1 Viewer)

[Ronald Rooij]

Hope someone can help. We are in Manaus, Brazil at the moment and it is almost 40C, so need the AC desperately.
The AC works intermittently. Cannot find the cause.
We have been at an AC shop and pressures are ok.

There is power at the AC fuse. But no 12v at the clutch. When tested with 12v straight to the clutch it engages and we get cold air.

When pushing the AC button on the dash the revs increases and I feel the ac clutch relay clicking.
Sometimes the AC starts cold but after 5 mins or so it stops working, it might go on again a few minutes later.
Engine temperature is normal.

I wanted to switch the ac clutch relay for another one for testen, but it is impossible to remove or is there a trick to do so?

Appreciatie some suggestions

Ronald

 

[Rusty Marlin]

Check the low pressure switch, they get flakey and will do as you discribe with intermittent contact.

 

[stuntheavy]

Have you verified system pressures?

Too low, and you’ll basically dump the low side pressure low enough to have the sensor cut out the ac clutch. Not uncommon to have a slow leak on a vehicle of this age.

Too high (if someone has recently ‘serviced’ the ac) and in high ambient temps, you’ll spike the high side high enough that it will cause the ac clutch to kick out.

I wouldn’t apply B+ to the clutch for any amount of time before verifying this. Could get real exciting

 

[OffRoadScott]

I had a similar situation not too long ago. The switch in the climate control unit on the dash (A/C button) was not staying engaged. My mechanic found another control and de-soldered a switch and soldered it into my HVAC/Climate control.

HVAC/Climate Control

Found this one on Ebay here in the US, might want to check the part out threads in the Classified section here on MUD.

If you can locate another climate control for your rig replace it or repair the switch. Unfortunately the climate control unit as a whole is not available new.

 

[smritte]

The AC works intermittently. Cannot find the cause.
We have been at an AC shop and pressures are ok.

This is the problem. "If" the pressures were good during the visit to the AC shop, There's very little anyone can do other than guess.
Assuming the pressure was actually good, you already eliminated refrigerant as an issue. That also pretty much eliminates the entire ac system except the TXV. I have had TXV's intermittently stick.

If were going to guess, that leaves the electrical system and TXV. I chased an intermittent issue on my buddies 97 LX for about a year. Why so long? because every time I showed up, it was working perfectly. This was the one with the TXV issue, during testing the TXV would fluctuate normally. Finally it stuck closed.

I feel your pain. Intermittent problems suck. AC has been one of my specialties professionally since the late 70's. Your best bet is to get it checked out while the problem exists, otherwise your just randomly throwing parts at a 25 year old vehicle.

 

[Ronald Rooij]

I Just ran the car from cold start. AC is ok. When engine gets hotter the AC stops.
I shorted the low pressure sensor at the connector, no difference. AC clutch does not engage. I assume the low pressure sensor is ok then as there is probably continuïteit at the sensor.
Pressure sensor is only two wires.

How, where is high pressure sensed?

If engine temp gets to high (it is normal at the dial) it should also shut off the AC. Is there a different sensor for this?

 

[Ronald Rooij]

This is the problem. "If" the pressures were good during the visit to the AC shop, There's very little anyone can do other than guess.
Assuming the pressure was actually good, you already eliminated refrigerant as an issue. That also pretty much eliminates the entire ac system except the TXV. I have had TXV's intermittently stick.

If were going to guess, that leaves the electrical system and TXV. I chased an intermittent issue on my buddies 97 LX for about a year. Why so long? because every time I showed up, it was working perfectly. This was the one with the TXV issue, during testing the TXV would fluctuate normally. Finally it stuck closed.

I feel your pain. Intermittent problems suck. AC has been one of my specialties professionally since the late 70's. Your best bet is to get it checked out while the problem exists, otherwise your just randomly throwing parts at a 25 year old vehicle.

What is TXV?

 

[Ronald Rooij]

Found it. Looks like a big job to get it replaced. How does it work. It Just closes the flow and this would cut the ac clutch due to high pressure?

 

[Ronald Rooij]

I meant I ound what TXV is.

Engine cooled down a bit, started again, AC is working.

When engine temp gets higher (and maybe pressure) ac clutch disengages again.

When at the AC shop they only tested low pressure side and said it was ok. I am not a specialist so we accepted this. We had done 2000k with fulltime AC the last few days without any problems so we only expected a system with less refrigerant.

Looking glass shows white foam when ac runs

 

[smritte]

Off the top of my head, I don't remember the exact spot on the LX. The back of my mind is its near the Drier.
When the AC quits, is the compressor off? The high pressure switch is actually called a dual pressure switch If the system is very low or too high, it opens the circuit.

You need some basic understanding of AC end electrical. You also need to have the system not working when you test. Otherwise everything you test will test good.
You need to be reading the pressure and know where their suppose to be.

Unfortunately your vehicle has "Automatic AC" What that means is more things that can fail.
I can give multiple examples of each of your parts I have replaced. That doesn't mean any of it is broken on yours. What that means is, just because someone else needed that part doesn't mean you do. You can keep throwing parts at it and hope for the best but, these systems don't have a "common failure" and you cannot compare to a common failure in a diffrent make/model.

 

[smritte]

When at the AC shop they only tested low pressure side and said it was ok. I am not a specialist so we accepted this. We had done 2000k with fulltime AC the last few days without any problems so we only expected a system with less refrigerant.

Looking glass shows white foam when ac runs

Trying to keep up. was doing research while at work.

The AC shop only tested low side.
Their idiots. Don't go back to them. High side tells you more.
You NEED a good set of pressure readings properly taken and not at idle.
Foam at site glass can be misleading but, without seeing it says low charge. IF the idiots took a high side reading, it would have been obvious.

 

[smritte]

You really need this tested properly by a shop that knows what their doing.

 

[truthdetector]

Coolant temp sensor on head telling the A/C to turn off due to high-temp? If not actually too hot, then maybe that sensor is failing?

 

[jpoole]

If it's consistently going off when above a certain temperature and back on when below then I'd put it being overcharged high on the list of possibilities. Simply reducing the refrigerant in the system until it stops going into over-pressure mode can allow the AC to stay on continuously. If high pressure and overcharging are not your issue then reducing refrigerant won't help and could just throw off your charge balance and cause other issues. Ideally you take this in to a shop or use gauges and refrigerant collection equipment as you dial in the pressures.

If you are in a situation where you can't get to a shop, your passengers are in melt down, etc. and you are pretty confident that the system may be overcharged then you can let some coolant out a little at a time to relieve pressure until the AC stays on. I wouldn't try this if you can get to a shop and I also wouldn't do it unless you are comfortable re-adding refrigerant to the system via a can, if you let too much out. The process is pretty quick/simple, you remove a cap and push the little pin to release some refrigerant (and pag oil that's in it). The fill ports on the AC system work like those on a car tire. The refrigerant stuff smells bad and will spray everywhere. A towel over the top and a glove on your hand will keep you from living with the annoying smell longer than you want. A few brief (less than a second) releases at a time and you should see that the AC will stay on at higher and higher temps until it stops cutting off.

It's worth saying that it is helpful to have real-time engine temp monitoring ability so that you can have a clear sense of when the AC is cutting off and if you are making progress with your refrigerant level tuning. You also want a strong fan clutch and clean condensor/radiator plus a fan shroud, foam between the radiator and core support, etc. If your 80 is running hot (around 220 F coolant temp kills AC), air flow over the condensor is insufficient, etc. then you may have a good refrigerant charge level and simply be overheating things and causing a shut-down that way. This is where going to a shop makes a lot of sense since we don't really know what the problem is and you don't want to start messing with stuff and making things worse unless you have little to lose or know what you are doing.

Before one road trip, when I had recently gotten my 80 and the AC wasn't sorted, I overcharged the AC system. It would cut off only when the engine bay was really heat saturated. I bled off a little refrigerant at a couple of fuel stops and was able to solve the problem and prevent the AC from turning off for the rest of the trip. I had the benefit of knowing that all else was fine and that the only thing that had changed was my recent addition of refrigerant to the system.

 

[Ronald Rooij]

If it's consistently going off when above a certain temperature and back on when below then I'd put it being overcharged high on the list of possibilities. Simply reducing the refrigerant in the system until it stops going into over-pressure mode can allow the AC to stay on continuously. If high pressure and overcharging are not your issue then reducing refrigerant won't help and could just throw off your charge balance and cause other issues. Ideally you take this in to a shop or use gauges and refrigerant collection equipment as you dial in the pressures.

If you are in a situation where you can't get to a shop, your passengers are in melt down, etc. and you are pretty confident that the system may be overcharged then you can let some coolant out a little at a time to relieve pressure until the AC stays on. I wouldn't try this if you can get to a shop and I also wouldn't do it unless you are comfortable re-adding refrigerant to the system via a can, if you let too much out. The process is pretty quick/simple, you remove a cap and push the little pin to release some refrigerant (and pag oil that's in it). The fill ports on the AC system work like those on a car tire. The refrigerant stuff smells bad and will spray everywhere. A towel over the top and a glove on your hand will keep you from living with the annoying smell longer than you want. A few brief (less than a second) releases at a time and you should see that the AC will stay on at higher and higher temps until it stops cutting off.

It's worth saying that it is helpful to have real-time engine temp monitoring ability so that you can have a clear sense of when the AC is cutting off and if you are making progress with your refrigerant level tuning. You also want a strong fan clutch and clean condensor/radiator plus a fan shroud, foam between the radiator and core support, etc. If your 80 is running hot (around 220 F coolant temp kills AC), air flow over the condensor is insufficient, etc. then you may have a good refrigerant charge level and simply be overheating things and causing a shut-down that way. This is where going to a shop makes a lot of sense since we don't really know what the problem is and you don't want to start messing with stuff and making things worse unless you have little to lose or know what you are doing.

Before one road trip, when I had recently gotten my 80 and the AC wasn't sorted, I overcharged the AC system. It would cut off only when the engine bay was really heat saturated. I bled off a little refrigerant at a couple of fuel stops and was able to solve the problem and prevent the AC from turning off for the rest of the trip. I had the benefit of knowing that all else was fine and that the only thing that had changed was my recent addition of refrigerant to the system.

Can I test overpressure/underprssure by bypassing the sensor near the drier for just a sec or so? If the clutch then engages it would be a charging issue?

 

[jpoole]

It sounds like you could do that but other folks will have to weigh in, or you'll have to test/research, to nail down how to test it.

I've not had to interact with the high pressure switch on an 80 so don't know for sure where it's located or what signals it sends to the computer to indicate high pressure. If you know where the switch is you could test to see what it's resting state is (continuity or no continuity across what I assume are two contact points/wires?) and then you could go from there. If it's a two wire system that is open (no continuity) when pressure is NOT high then simply unplugging the sensor may tell the computer that pressure is not too high and would turn the AC back on when it's shut off. If the high pressure sensor is closed (continuity) when pressure IS low and then opens when pressure IS high then you may need to make a jumper to keep the circuit closed to see if that keeps the AC on, etc. Beware of running the system for very long in an over-pressurized state as damage seems likely to occur.

There could be the risk of causing electrical system damage by unplugging the sensor while the vehicle is operating, even if risk is unlikely/minimal, but you could possibly check the circuit state with probes without plugging/unplugging the sensor in, etc.

Overall I think this testing and exploration is a good course of action to take as it should be a quick/easy way to zero in on where the issue is. I share some of the above because I don't know how comfortable you are with running tests like these and I want to make sure I don't push you towards making things worse or wasting time. Even if you end up at a shop or hit a dead end it would be good to know if the high pressure indicator is what is shutting the system off as that rules out all of the other possible causes mentioned in this thread, etc. Likewise, if the pressure switch is not at play you can shift focus to the next easiest part of the system to test.

 

[Ronald Rooij]

I lowered the pressure in the system, no solution. Bypassing the sensor also not a solution. It is only 2 wires, do not know if it does both high and low pressure.

There is also a AC water temp switch which is normally open. Finally found it. When the engine cools down I will pull this one. Leaving it disconnected should stop the clutch disengaging as well.

Tried every thing else. All relays seem ok. The clutch consistently disengages when the engine gets warmer. It is here in Manaus almost 40C and in the engine bay even warmer.

 

[jpoole]

Did you put a meter on the high pressure sensor to see if it's changing state? Most likely it's open when pressure is normal and then closed (continuity) when pressure is high. You need a multimeter capable of checking ohms (most/all are).

Do you have real time engine coolant temp numbers? Can you share what the highest coolant temps are when the AC is on and then what they are when the AC shuts off?

The fact that the AC shuts off with heat makes me think that you are on the right track with pressure/temp triggered disabling but I also think it's worth being thorough enough to confirm that your tests are proving what you think they are since you haven't found the problem.

Is there an option of taking it to a knowledgeable auto AC shop and reliably triggering the issue so that they can check things when it's in it's broken state?

 

[Ronald Rooij]

From the wire diagram the pressure switch is normally closed. 2 Switches are drawn in 1 box so I assume it is both low and high pressure. I have no means of testing the sensor, only to bypass it with a jumper.
This was not causing the issue.

As the AC works when the engine is cold(er) I skipped all the other sensors in the fault analyses tree.

I first suspected the clutch relais. It clicked but might not allow current to flow or only poorly. You can feel/hear it clicking with the engine off, but it is almost impossible to remove for testing. So I left it.

Next was the water temp switch. This is drawn as NO in the EWD. I just could not find it. Found it through another mud topic. First (wrong!) removed the water temp sensor. Not a great idea as the connector was brittle. The temp switch is on the right of this sensor right above the oil filter.
It is a big car and a big engine but the sensors are almost all hard to reach, certainly when the engine is hot. It took some time waiting for the engine to cool down.
As the switch is NO, taking off the connector should do the trick.

It probably was faulty As the AC stays on now. Engine temp is normal.
At first opportunity I will replace the switch.

Thanks to everyone contributing.

 

[mudgudgeon]

As the AC works when the engine is cold(er) I skipped all the other sensors in the fault analyses tree.

Did you confirmed engine coolant temperatures? And not just relying on the gauge on the dash?

40⁰c is gonna be testing your cooling system.

You assume the sensor is faulty?
If it's working as intended, you may have just masked a bigger issue than passenger comfort.