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1990 LS400 A/C Electrical problem

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Old 05-12-11, 04:31 PM   #1
tenchu
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Default 1990 LS400 A/C Electrical problem

I just picked up a 90 LS400 that the AC doesn't work on.

I took it to an AC shop, and they said that the A/C system looks mechanically sound (compressor, lines, etc) and that there is refrigerant in the lines, but that there is an electrical problem that is not telling the compressor to engage. The AC button lights up, and the blower motor works.

This shop said they don't work with electrical issues so I would have to take it to another shop. I can do electrical stuff, I just don't have the proper tools to work with A/C which is why I took it in.

Is there any common problems with the A/C in these cars that I should know about, or does anyone have and ideas on where I should start?
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Old 05-12-11, 04:55 PM   #2
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You may have refrigerant in the system, but you don't have enough. You need to get a refrigerant recharge. The electronics in your a/c system contains a relay which will not let the compressor engage if your refrigerant gets too low. This is to protect your compressor.
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Old 05-12-11, 05:00 PM   #3
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Quote:
Originally Posted by somnoboy View Post
You may have refrigerant in the system, but you don't have enough. You need to get a refrigerant recharge. The electronics in your a/c system contains a relay which will not let the compressor engage if your refrigerant gets too low. This is to protect your compressor.
Okay, I still have a can of R134 in my closet I can use, i'll just have to go buy a gauge for it. But worst case scenario, if the lines are full, or filling them doesn't fix the problem, do you have any other suggestions? I taking a 1700 mile drive in less than two weeks, so I really want to get the A/C up and running.

PS- I realize the car is originally R12, apparently the car has already been retrofit for R134A according to the A/C shop.
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Old 05-12-11, 08:19 PM   #4
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Check for codes and then you'll know what to look at. http://www.lexls.com/tutorials/air/accodes.html
As somnoboy said, the refridgerant can be low, it won't turn on without the correct pressure. This just happened to someone, I can't remember who, but maybe you can search for it. It might help ya.
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Old 05-13-11, 03:38 AM   #5
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Quote:
Originally Posted by deanshark View Post
Check for codes and then you'll know what to look at. http://www.lexls.com/tutorials/air/accodes.html
As somnoboy said, the refridgerant can be low, it won't turn on without the correct pressure. This just happened to someone, I can't remember who, but maybe you can search for it. It might help ya.
Actually, it was me that this happened to. Yes, a full writeup documenting the agony is on here, if you search. I wouldn't bother with the DIY can. This is the sort of thing that you need to take to a mechanic who handles A/C issues. You may have a slight leak in the system. If so, simply have the mechanic recharge it once a year and forget about it. Or, you could go and actually have an expert hunt down the slight leak in the system and have it fixed right once, but this will cost a small fortune.

Either way, please do keep us posted as to what transpires.
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Old 05-13-11, 07:28 AM   #6
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If they said it was an electrical issue, then I assume they already checked that it had the correct charge, so I don't think adding any more refrigerant is going to help. You might want to check somnoboy's thread and try bypassing the relay to see if you can get the compressor to spin.
http://www.clublexus.com/forums/ls40...r-problem.html
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Old 05-13-11, 09:56 AM   #7
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Thanks for the suggestion deanshark, but unfortunately I don't have a working climate control LCD to be able to check the AC troublecodes.

vgb, i'll give that a check!
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Old 05-13-11, 11:51 AM   #8
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Thank you 91LS400vgb for that link! I bypassed the relay as suggested, and the compressor clutch engaged, so I grabbed my can of R134A, and got to filling (also found a problem). AC blows cold now, everything is in working order.

But, the low side valve leaks when the cover is off (so i'm sure it slowly leaks when the cover is on, hence the lack of refrigerant) but at least I can be cool on the 1,700mi drive home now, and worry about fixing the leak when I get there.

Thanks again!
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Old 05-13-11, 12:48 PM   #9
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Scratching my head wondering why the shop thought it was an electrical issue. Ok - you might be able to fix that low side leak by replacing the low side r12-r-134a adapter. You mentioned that the car was converted to r-134. Therefore, it should have an adapter. The adapter screws onto the old r-12 schrader valve. Now, it's possible that the r-12 schrader valve core is leaking and the refrigerant is either leaking around the threads of the r-134 adapter or from the adapter's schrader valve. So, you might want to try replacing the adapter with a new one. The new one should have some kind of thread sealer on it. Also, from experience, don't overtighten the adapter or you'll have trouble trying to hook a manifold gauge onto it.
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Old 05-13-11, 01:00 PM   #10
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Quote:
Originally Posted by 91LS400vgb View Post
Scratching my head wondering why the shop thought it was an electrical issue. Ok - you might be able to fix that low side leak by replacing the low side r12-r-134a adapter. You mentioned that the car was converted to r-134. Therefore, it should have an adapter. The adapter screws onto the old r-12 schrader valve. Now, it's possible that the r-12 schrader valve core is leaking and the refrigerant is either leaking around the threads of the r-134 adapter or from the adapter's schrader valve. So, you might want to try replacing the adapter with a new one. The new one should have some kind of thread sealer on it. Also, from experience, don't overtighten the adapter or you'll have trouble trying to hook a manifold gauge onto it.
I thought about trying that as well, but I'm gonna wait for now, I have a bunch of more important things to do (like the timing belt) before I hit the road. Once again, thanks for your help!
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Old 06-21-11, 11:26 PM   #11
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Anybody help with 134A capacity ounces for '93 LS400???
And location of High Side port?
And why I have TWO Low Side ports or is one really hte High Side with a mismarkd "L" cover???
BTW, same experience with no compressor at low refrigerant level... lost most of mine over the winter and am now just starting to deal with it... with engine running, pressed A/C button and began to add 134A [at the "top" Low Side port, and sure enough, it wasnt long until the compressor kicked on... have added 4oz system sealant and 2 X 12oz cans 134A... but I need to know what the capacity really is. Found an on-liine chart that says for '93 LS400 with single A/C, it's 32-35 ounces.... y'all agree???
TIA
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Old 06-22-11, 02:53 PM   #12
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The 93 LS400 uses 33.5 oz. of R-134a and 5.25 oz. of PAG-46 oil.

As for the two ports, my car is different because it's a 91 and uses R-12. However, I also have 2 low side ports. I was able to hook a low side gauge to the lower of the two (and closer to the firewall) and charge it. Your 93 may be different so I can't tell you for sure.
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Old 08-01-11, 04:57 PM   #13
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In regards to the oil that is combined with the refrigerant. How do you know on how much oil to add? if you have any in the system to begin with.
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Old 08-07-13, 11:54 AM   #14
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I am experiencing the same issue. Turn on ac light stays green. I recently had leak and come to find out the previous owner used rtv instead of a n o ring . Problem solvee. I thought. So i took it in to get charged. It held vacuum, passed leak test but compressor clutch never engaged. Does anyone know what couls be the issue. 1990 ls400 retrofitted.
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Old 08-07-13, 04:38 PM   #15
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keep in mind that if your LS400 A/C system has proper refrigerant type and amount installed, and still the compressor will still not engage, the most common reason on LS400 is not an A/C problem at all, it is failing ECU capacitors!
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Old 08-07-13, 04:38 PM
 
 
 
 
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