SOLVED. PART 2...A/C light blinking mystery (1 Viewer)

[flintknapper]

I just did more jumping. I first pressed A/C button and fan on, A/C light stays on because switch is unplugged. Then based on the numbers in switch picture above....I jumped 1 and 2 and compressor comes on for three seconds and A/C light blinks.

Like before, I then turn A/C control button off then back with light staying on. I jump 1 and 4 and compressor comes on then off every three seconds as long as I keep jumper on it.... but A/C light does stays on not blinking.

Still can’t seem to jump fan on but I saw it on before. I hope I haven’t fried anything jumping wrong terminals.

No you haven't fried anything. I've been looking at my EWD (for a 99 LX470) and confirming the circuitry. You've gotten out a little ahead of me....but the information is useful.

Presumably your 2000 is wired the same. From what I can tell....the components I suspect now are the Condenser Fan Relay and/or the Pressure switch itself.

Line 3 comes out of the Center ECU goes to the Trinary Switch (pressure switch) and IF the switch has enough pressure and is closing the normally open contact then that circuit continues on (as line 2) to the A/C Condenser Fan Relay, from there it goes to the Magnetic Clutch Relay and finally to the Compressor Clutch and Lock Out Sensor.

Line 1 comes out of the Center ECU goes to the Trinary Switch to be completed to ground (as line 4).

So that is why I wanted you to jump across 1 and 4 (to create a known ground).

You have swapped out the Clutch Relay but not the Fan Relay and the circuit has to go through both. So that would be my next thing in the process of elimination. If that does not solve the issue....then it points squarely to the pressure switch itself or the wiring somewhere along the way.

 

[BullElk]

You have swapped out the Clutch Relay but not the Fan Relay and the circuit has to go through both. So that would be my next thing in the process of elimination. If that does not solve the issue....then it points squarely to the pressure switch itself or the wiring somewhere along the way.

I just tried a good fan relay from other 2000 LX. No change. Same blinking light after three seconds. And both relays had the same reading of about 80.0 ohms between same small pins. I have had a bad relay in my other LX that I replaced but it did not keep the compressor from working properly.

Guess I need to take it back to my indy friend to evacuate and try a new pressure switch. This is becoming more fun that ever. But I am not in the hospital or in prison...or in a prison hospital so things aren't too bad.

 

[flintknapper]

I just tried a good fan relay from other 2000 LX. No change. Same blinking light after three seconds. And both relays had the same reading of about 80.0 ohms between same small pins. I have had a bad relay in my other LX that I replaced but it did not keep the compressor from working properly.

Guess I need to take it back to my indy friend to evacuate and try a new pressure switch. This is becoming more fun that ever. But I am not in the hospital or in prison...or in a prison hospital so things aren't too bad.

^^^^^

That's the Spirit.

Never let yourself think 'things couldn't be worse' (believe me THEY CAN). Or ask yourself 'What Next' (because odds are...you'll find out).

Count your blessings, keep your chin up and soldier on.

Some things on vehicles are difficult to diagnose. A/C being chief among them....since so MANY things can go wrong. Taking your time to go through it methodically and eliminating (as much as it is possible) the different components can be arduous. Even defeating at times, but there is an answer if we just stay after it.

So....logically, I'd say you've worked yourself to a point where the pressure switch itself is faulty OR the wiring somewhere in the circuit. We can't even rule out the Center ECU but it seems unlikely.

I agree that the reasonable next step is to replace the trinary switch. The intermittent function of the condenser fan sort of makes it extra suspect anyway (assuming your fan is OK).

 

[ttahara]

2000 LX. A/C light blinks after compressor engages for about three seconds then disengages.

What I DO know so far...... thanks to the generousity, knowledge and guidance of @flintknapper is......

--The compressor will engage fine when jumping the relay.
--The relay is good (tested in other vehicle)
--Front A/C amplifier is good (tested with known good source)
--Rear A/C amplifier is good (tested with known good source)
--Pressure switch is good
--Freon has been evacuated, filled properly and tested with no leaks

Anything else you guys may have run into or anything else to check that comes to mind ??

Thanks a

This would activate the compressor 'lock out' sensor and prevent the clutch from engaging alright, but in an earlier test the OP jumped the unit and states it runs fine. We had discussed that when trying to sort this out via PM, but ultimately decided it would be best to bring the issue to the general forum in hopes of soliciting a solution.

I'm not intimately familiar with the circuit (from relay to clutch) but I would think if he can jump it from that point that the Lock Out is probably not the issue, but not 100% sure of that.

IF the sensor detects a significant difference between engine speed and compressor speed, it assumes the compressor is trying to seize. So in an effort to save the serpentine belt from shredding, it disables the clutch.

I had this same issue when I worked at a dealership, I went through the same procedure you did, tested all the circuits and swapped parts, the lock out sensor was bad.

 

[BullElk]

I had this same issue when I worked at a dealership, I went through the same procedure you did, tested all the circuits and swapped parts, the lock out sensor was bad.

Is that one with the compressor or can it be replaced separately, if I can get to it ?

Ahhh... I see on another thread where the sensor cannot be replaced separately. Would have to replace entire compressor......If that is the probem.

 

[flintknapper]

I had this same issue when I worked at a dealership, I went through the same procedure you did, tested all the circuits and swapped parts, the lock out sensor was bad.

We have discussed that possibility too and you could be right.

This could be bypassed temporarily to see if it would allow the compressor to run. IF so...then we would know all other components are at least working, but the bad news is that would be a new compressor whether the compressor was trying to seize or the sensor was at fault.

The sensor is integral to the compressor. It IS available separately but the cost of it and replacing it make a new/reman compressor the better deal.

 

[BullElk]

This could be bypassed temporarily to see if it would allow the compressor to run.

FYI....Not sure if this pertains to the lock out sensor but the compressor will run when jumping the relay and has never really seized up did any grinding with clutch like I have seen once before.

 

[flintknapper]

FYI....Not sure if this pertains to the lock out sensor but the compressor will run when jumping the relay and has never really seized up did any grinding with clutch like I have seen once before.

Yes, and that is why I initially dismissed the idea of it being the Lock Out Sensor, but I don't know if jumping past the relay negates the action of the ECU to cut the power to the clutch. It might be worth the effort to cover all the bases and disconnect the harness at the compressor, jump that and retest. First calling for the A/C from the dash (per normal procedure) and then if that doesn't work, jumping the relay also.

IF the compressor comes on and runs with the Lock Out bypassed then we have our answer. If it doesn't then it puts it back in the court of the pressure switch. After that...there is only wiring or the Center ECU.

I don't know how difficult it is to reach the harness....but I bet its buried pretty good. Hope you have small hands, skinny arms and are flexible.

 

[BullElk]

Dadgumit

 

[flintknapper]

Dadgumit

 

[BullElk]

Regarding the lock out sensor as it relates to speed of compressor and engine, I did notice when the compressor was jumped for recharging with freon, the engine was really dragging more than it should with a properly working system. Curious if this pointed to bad lock out sensor.

 

[SHIfTHEAD]

I recall last summer I had the blinking AC button in my control screen and noticed the AC was not blowing cold any longer. I found that one cause is when the engine temps get too high the ECU will disable to compressor as it adds heat to the radiator as the air cools the condenser. I later found that the thermostat was stuck mostly closed, so the average temps of 210 and spikes to 230 were not normal. Not I stay in the 190s most of the time. So I'd recommend that you run an ODB2 app and confirm your temps, because my analog gauge in the cluster never got much past exactly center of the dial.

 

[medtro]

--Pressure switch is good

I just tried a good fan relay from other 2000 LX. No change. Same blinking light after three seconds. And both relays had the same reading of about 80.0 ohms between same small pins. I have had a bad relay in my other LX that I replaced but it did not keep the compressor from working properly.

Guess I need to take it back to my indy friend to evacuate and try a new pressure switch. This is becoming more fun that ever. But I am not in the hospital or in prison...or in a prison hospital so things aren't too bad.

I thought you said pressure sensor is good in the first post.

 

[flintknapper]

I thought you said pressure sensor is good in the first post.

I think that was an assumption. At worst a 'starting point' and as more testing is performed....diagnostic outcomes can change. We simply don't know for sure at this point.

 

[BullElk]

I thought you said pressure sensor is good in the first post.

The indy did put a mulitmeter on the switch and just said it was good. I could not get a good ohms reading for whatever reason. I did jump compressor two different ways resulting in compressor engaging in two different manners. Both ways the compressor would only stay on for three seconds. But could not jump the condensor fan so I really don't know if all three mechanisms or circuits are working on the switch.

The fact that the compressor stays on for only the very consistent three second interval every time I try to engage it via the way its designed (not jumping relay) makes me think something like the lock out speed sensor is sending the same signal every time for a reason. Whether working properly due to engine speed or just broken.

 

[flintknapper]

The indy did put a mulitmeter on the switch and just said it was good. I could not get a good ohms reading for whatever reason. I did jump compressor two different ways resulting in compressor engaging in two different manners. Both ways the compressor would only stay on for three seconds. But could not jump the condensor fan so I really don't know if all three mechanisms or circuits are working on the switch.

The fact that the compressor stays on for only the very consistent three second interval every time I try to engage it via the way its designed (not jumping relay) makes me think something like the lock out speed sensor is sending the same signal every time for a reason. Whether working properly due to engine speed or just broken.

So maybe worth trying to bypass to test....before looking to the pressure switch?

IF you do the pressure switch first and it isn't the cause....you'll have to evacuate the system twice. If bypassing the Lock Out corrects it...then of course its new compressor time....but only one evacuation and recharge and no parts added that might not have been needed.

 

[ramangain]

Wouldn't a quick pressure check by now be prudent?

"Trust but verify"

 

[medtro]

The indy did put a mulitmeter on the switch and just said it was good. I could not get a good ohms reading for whatever reason.

Out of range (open circuit) because the pressure is not high enough since the compressor ran for 3 seconds only? This would be a good test on your vehicle with working AC.

 

[flintknapper]

Wouldn't a quick pressure check by now be prudent?

"Trust but verify"

If we were at a point where we could run the system to stabilization yes. But currently the only thing pressure would affect would be the Trinary Switch (pressure switch). IF the system had less than 28 psi AND the pressure switch is working then it would not allow the clutch to engage. Similarly IF the pressure were over 455 psi (that's a LOT) the high pressure side of the switch would again cut the clutch out.

Since we have no 'known' leaks it doesn't seem likely that low pressure would be the issue. It wouldn't hurt to put a set of gauges on it and record the 'static' pressure. IF at least 50 psi then we know there is enough pressure to satisfy the minimum for the low side of the pressure switch and it confirms there is some amount of liquid refrigerant in the system. But personally, I wouldn't.

 

[flintknapper]

Out of range (open circuit) because the pressure is not high enough since the compressor ran for 3 seconds only? This would be a good test on your vehicle with working AC.

Or with static pressure high enough to close the normally open switch. Compressor would not have to be running for that. But the ambient temp and refrigerant charge would need to be sufficient to create around 50 psi static pressure AND the contacts in the pressure switch be capable of closing. That is what makes diagnosing pressure switches so difficult. Mechanically, you don't know their condition.