AC troubleshooting in a 99 LX?

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I would appreciate some insight into where to start troubleshooting my recent AC issue in my 99 LX. I am trying to get an appointment at a shop to check the pressures, but until then I have been doing some other troubleshooting.

When I bought it in June 2020 (from Phoenix) the AC worked great and has worked fine until just recently.
  • I don't hear the compressor come on at all.
  • When I have someone press the AC button, I don't hear any relays click in the JB.
  • Followed the FSM to check the sight glass and saw nothing. No bubbles. Nothing.
  • Diagnostic mode showed CODE 23
    • Open in pressure sensor circuit
    • Abnormal refrigerant pressure
Reading through all the other threads on the AC, it seems like low refrigerant is a common issue and if it's too low the compressor won't come on. What has me confused is that back in October 2020, I replaced the high pressure discharge line (above the radiator) with OEM because it was leaking. I took it to a shop to evacuate the system and then recharge it after I replaced the line. They added UV dye as well, so as of October, it was fully charged. If there was a significant enough leak to let all that refrigerant out, wouldn't I see UV all over the place somewhere? And the only change to the system was that line and there don't appear to be any leaks there.

I tried to use Tech Stream to trigger the A/C but couldn't figure out how. Maybe that's only on the new 100 series with NAV?

I also tried the low-tech suggestion from @flintknapper on another thread to depress the shraeder valve on the low-pressure line and got a very forceful discharge.

I know some people have had issues with the magnetic clutch relay and on the newer models it's almost impossible to get to. But on the 99 it appears to be easily replaceable?

It just seems weird that it would stop all of a sudden. The PO did need to top off the refrigerant back in 2014. But it's been running fine since then.
 

flintknapper

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I would appreciate some insight into where to start troubleshooting my recent AC issue in my 99 LX. I am trying to get an appointment at a shop to check the pressures, but until then I have been doing some other troubleshooting.

When I bought it in June 2020 (from Phoenix) the AC worked great and has worked fine until just recently.
  • I don't hear the compressor come on at all.
  • When I have someone press the AC button, I don't hear any relays click in the JB.
  • Followed the FSM to check the sight glass and saw nothing. No bubbles. Nothing.
Getting some pressure readings is indeed the correct place to start given the information provided.

  • Diagnostic mode showed CODE 23
    • Open in pressure sensor circuit
    • Abnormal refrigerant pressure

Correct. Trouble Code 23 basically means:
1. You have an 'open' in the wiring, corrosion at a connector or a short.
2. The pressure switch itself 'binary switch' is faulty.
3. You actually have less than 25-28 psi in the system in order to satisfy the low pressure switch. It will disable the compressor clutch if there is too little or too much pressure in the system.

Reading through all the other threads on the AC, it seems like low refrigerant is a common issue and if it's too low the compressor won't come on. What has me confused is that back in October 2020, I replaced the high pressure discharge line (above the radiator) with OEM because it was leaking. I took it to a shop to evacuate the system and then recharge it after I replaced the line. They added UV dye as well, so as of October, it was fully charged. If there was a significant enough leak to let all that refrigerant out, wouldn't I see UV all over the place somewhere? And the only change to the system was that line and there don't appear to be any leaks there.

A couple of places where leaks are hard to detect are the Evaporator and the lines to rear A/C *if equipped*. The bottom of the evaporator can leak and the dye will drip out the condensation drain line and go unnoticed. Rear A/C lines can corrode and just simply leak in an area you don't normally look.
I tried to use Tech Stream to trigger the A/C but couldn't figure out how. Maybe that's only on the new 100 series with NAV?

Can't help you with that....but shouldn't be necessary.
I also tried the low-tech suggestion from @flintknapper on another thread to depress the shraeder valve on the low-pressure line and got a very forceful discharge.

Tells us some amount of liquid refrigerant is in the system...which is good, but doesn't tell us how much.

I know some people have had issues with the magnetic clutch relay and on the newer models it's almost impossible to get to. But on the 99 it appears to be easily replaceable?

Yes, a whole host of things could be the issue. But a pressure test will separate the possibilities into, mechanical/electrical/refrigerant charge.
It just seems weird that it would stop all of a sudden. The PO did need to top off the refrigerant back in 2014. But it's been running fine since then.

Agreed. The system suddenly stops without warning or diminished performance. Suggests an electrical issue...but any competent shop is going to want pressure readings first, even if just 'static' pressure.
 
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Jaz

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Thanks for taking the time to go through my long post Flint. I’ll try and get the system checked on Monday and report back.
Get yourself a set of manifold gauges so you can see what is going on. The FSM has a good section on reading the gauges and diagnosing issues.
 
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Get yourself a set of manifold gauges so you can see what is going on. The FSM has a good section on reading the gauges and diagnosing issues.
I am going to pick up a loaner set at Autozone on my way home. I've been watching some videos and reading on here about what different readings could mean. Is there any thing I need to look out for? Any warnings? From what I can tell you just hook up the quick connects and then screw down the fitting to open the valves and check pressure?
 
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Well, I picked up the gauges and it looks like I am low on refrigerant? Looking at the FSM (and other videos I found online) they want you to test with the engine running and the compressor cycling on and off. Since my compressor isn't coming on at all the pressures didn't change when I started the engine. Thoughts? I have an appointment with a shop on Monday to check it over and recharge if needed. But I thought I would at least try the free test first....


IMG_1900.jpg
 
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flintknapper

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Well, I picked up the gauges and it looks like I am low on refrigerant? Looking at the FSM (and other videos I found online) they want you to test with the engine running and the compressor cycling on and off. Since my compressor isn't coming on at all the pressures didn't change when I started the engine. Thoughts? I have an appointment with a shop on Monday to check it over and recharge if needed. But I thought I would at least try the free test first....


View attachment 2751281

Since your compressor is not running.....what you are looking at is referred to as the 'Static Pressure'. Generally it is not of much use for diagnostic purposes....but in this case it tells us you do not have enough pressure in the system to satisfy the low pressure switch.

Assuming the gauges are reasonably accurate and all else is functioning correctly, then the compressor clutch will not engage until you have 28-30 psi minimum in the system. You have a 'Binary Switch' aka 'Pressure Switch' that will not allow the compressor clutch to engage if the pressure is too low or too high.

Looking at the gauges...it appears you are right on the 'cusp'....but still too low. Were you to add a small amount of refrigerant...the pressure would build and IF all else is working....the compressor would come on.

I don't know what the ambient temperature was when you took the pressure readings...but for those static pressures to be right, it would have to be about 33°F outside....and I am confident it was warmer than that....right?

So yes, take it in....let them find out where your leak(s) are and let us know what they said.
 
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Since your compressor is not running.....what you are looking at is referred to as the 'Static Pressure'. Generally it is not of much use for diagnostic purposes....but in this case it tells us you do not have enough pressure in the system to satisfy the low pressure switch.

Assuming the gauges are reasonably accurate and all else is functioning correctly, then the compressor clutch will not engage until you have 28-30 psi minimum in the system. You have a 'Binary Switch' aka 'Pressure Switch' that will not allow the compressor clutch to engage if the pressure is too low or too high.

Looking at the gauges...it appears you are right on the 'cusp'....but still too low. Were you to add a small amount of refrigerant...the pressure would build and IF all else is working....the compressor would come on.

I don't know what the ambient temperature was when you took the pressure readings...but for those static pressures to be right, it would have to be about 33°F outside....and I am confident it was warmer than that....right?

So yes, take it in....let them find out where your leak(s) are and let us know what they said.

Ambient temps was 80* when I tested the pressure. I could go back over all the lines with a UV light but yeah, I will take it to a shop to find the leak. Just out of curiosity, how would a shop go about finding a leak? What tools do they use?
 

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Ambient temps was 80* when I tested the pressure. I could go back over all the lines with a UV light but yeah, I will take it to a shop to find the leak. Just out of curiosity, how would a shop go about finding a leak? What tools do they use?

At 80°F ambient....your 'static' pressure should have been around 86psi. (for R134a).

Shops will employ a variety of methods, depending on how easily (or not) a leak is detected.

They might begin with a visual inspection, follow that with a Halogen Leak Detector. They might choose to pressurize the system and use a leak detecting solution around fittings or other easily accessed areas. It might be necessary to inject dye into the system and look for leaks that way.
 
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Took it to a shop this morning and they couldn’t find a leak. They also said it passed the vacuum test with no leaks and they wanted $300+ to evacuate and refill. Seems steep.

another shop i talked to said that sometimes small leaks dont register on the vacuum test? If there is no leak though then I should not have lost any refrigerant right?

I have not checked the evaporator for UV leaks yet.
 
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Took it to a shop this morning and they couldn’t find a leak. They also said it passed the vacuum test with no leaks and they wanted $300+ to evacuate and refill. Seems steep.

another shop i talked to said that sometimes small leaks dont register on the vacuum test? If there is no leak though then I should not have lost any refrigerant right?

I have not checked the evaporator for UV leaks yet.
You have a leak if the refrigerant is no longer present. Now just need to find the leak, I prefer to use high pressure nitrogen to pressurize the system to and either listen or find it with spraying all lines with soaping water. If you don’t see anything you may have a leak in your evaporator which is a simple job to replace.
 
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I had a system that passed the vaccum test. It didn't leak when it was off and static because it was in the compressor. When its not on, one of the pistons just so happened to be in a spot over the leak. It would only leak when the compressor was running and moving.
 
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This is probably not the fine tuned to answer that I normally see on the forum, but since you have pressure in the system you don't have moisture and do not need evacuation. I would add a can of freon, watching the gauges, and once it's full I would drive it a bit and monitor performance.
 
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Did the shop leave the system empty when they returned it to you? The only way they could have vacuum tested it was if the system is empty. Sometimes leaks aren't obvious under vacuum as it pulls things together, then under pressure, they're pushed apart. Did they put it on a lift and check the lines to the rear unit? I'd borrow a vacuum pump and gauge set from Autozone and vacuum it down and charge it. I would probably put dye in it to assist in finding the leak(s).
 
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I once had a case where there was no leaks yet charge was needed. It was BMW and compressor had pressure relive valve which opened during excessive heat over 100F and car idling parked.

I didn't pay much attention, figured it's a case of me leaving car idle in a bad heat. Charged it and it was all good for about a month until it puke it again.

Then I started to look into it and it was a bad fan. Not enough cooling -> overheat -> overpressure.
 

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Did the shop leave the system empty when they returned it to you? The only way they could have vacuum tested it was if the system is empty. Sometimes leaks aren't obvious under vacuum as it pulls things together, then under pressure, they're pushed apart. Did they put it on a lift and check the lines to the rear unit? I'd borrow a vacuum pump and gauge set from Autozone and vacuum it down and charge it. I would probably put dye in it to assist in finding the leak(s).

^^^^

This.
 
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Did the shop leave the system empty when they returned it to you? The only way they could have vacuum tested it was if the system is empty. Sometimes leaks aren't obvious under vacuum as it pulls things together, then under pressure, they're pushed apart. Did they put it on a lift and check the lines to the rear unit? I'd borrow a vacuum pump and gauge set from Autozone and vacuum it down and charge it. I would probably put dye in it to assist in finding the leak(s).
I don't know if they emptied the system. I have not picked it up yet. Regarding renting a vacuum pump and gauge set, I think that might be above my skill/comfort level? I can certainly hook up one of those cans of R134a, but I think that's money down the drain if it discharged this much in 10 months. I'd rather pay someone to do it right but I don't think this shop is the one I want to take it to. I called another shop that seems pretty honest and knowledgeable about these AC systems, but I think I might go over it with the UV light again to see if I can see a leak somewhere.
 

flintknapper

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I don't know if they emptied the system. I have not picked it up yet. Regarding renting a vacuum pump and gauge set, I think that might be above my skill/comfort level? I can certainly hook up one of those cans of R134a, but I think that's money down the drain if it discharged this much in 10 months. I'd rather pay someone to do it right but I don't think this shop is the one I want to take it to. I called another shop that seems pretty honest and knowledgeable about these AC systems, but I think I might go over it with the UV light again to see if I can see a leak somewhere.

They emptied the system if they performed a vacuum test on it. Not possible to do it any other way.

Yes, take it to another shop and see what they say.
 

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