zukikat

Sorry for the length in advance but I really need some help!

Admittedly I'm an a/c repair noob but I've been successful numerous times solo so far on several other makes/models and observed and assisted with repairs on at least dozen 80's/90's Toyotas over the last 5 years and thought I had a handle on things, but...

After working great for the first 18 months I owned the car, my 1994 LS400's factory compressor seized up while I was on the interstate early last fall with over 200k on the car and I didn't have time to deal with it then. I couldn't turn the front clutch plate by hand at all, nor could the engine whenever the clutch tried to engage.

At that time when the AC button was pressed the AC compressor's clutch would try to engage, the front clutch disc would go maybe 1/4 turn at most, the engine would bog down heavily, the accessory belt would start to slip and squeal for 5-10 seconds, then the clutch would disengage and the AC light would begin flashing. Turning the system off and trying again would cause the same thing.
I know that some Toyota/Lexus models have a compressor rpm sensor and will disengage the clutch and then flash the AC button's light if they don't see the proper compressor rpm range while the clutch is engaged, and this is one of those models. Going through puddles in the rain in my old 1996 Camry with the AC on would make the belt slip and disengage the clutch and flash the AC light until everything dried out...

Over this past weekend I replaced this '94 LS400's seized original Denso compressor with a used Denso compressor from a '94 LS400 junkyard car that still had a lot of freon in it, hoping to revive the AC while also doing a timing belt and water pump replacement job on this same car.

Vacuumed the system for about an hour then let it sit for about 30 minutes, vacuum held up fine.

I moved the gauge set's yellow hose from the vacuum pump to the freon cylinder, opened the gauge set's low valve, and let the cylinder push into the system until the tank and system pressures balanced out, about 90psi this time, plenty enough to activate the system's low pressure switch and allow it to engage the clutch as needed.

Started the car, hit the HI fan button to fire up the AC, the clutch engaged, the indicated gauge set's low and high side pressures never changed, and 5 seconds later the clutch disengaged and the AC button's light began flashing.

*** What the heck??? I don't get it???

The compressor speed sensor plug on the back of the compressor IS plugged in.

How can you have an engaged clutch and a running compressor and the Low side not go low and the High side not go high???

I know that on some vehicles with "variable displacement" compressors that have an internal "refrigerant control valve" you can have a running compressor and no suction/pressure at its' minimum displacement while running, but I didn't think Lexus did that sort of thing at all???
My 2001 Volkswagen has a variable displacement compressor which had a failed internal "R.C.V" so I'm familiar with these symptoms on a system like the VW's use, but I didn't think Lexus did anything like that, especially in 1994???

I suppose it's possible that this used compressor has a broken shaft or some other wierdness but even if there was something else wrong, as soon as the clutch disc engages and starts spinning the compressor shaft at all, shouldn't the Lo and Hi pressures "do their thing"?
I mean, literally the clutch plate spins for 5-10 seconds and the gauges don't even flinch. They both stay static at the 90psi of freon the cylinder pushed into the system...

I then tried the "hold down the auto and temp down buttons and start the car" diagnostic sequence and got the proper beeps and all lights test passed and 00 for codes so the system thinks everything is working properly.

Note that on this 1994 model LS400 there are two schraeder valves at the firewall. One further forward and higher up than the other. Only one had a cap on it and the letter L on the cap so I tried that one first. Out of confusion, after the gauges didn't respond I tried the other one and got the exact same result.
Which one of those two is the correct Low side fitting for this car?

Thanks in advance for any suggestions on why this system is behaving as it is now!

Thomas

zukikat

AC clutch engages when the AC system is turned on, the compressor's clutch plate begins spinning and runs as expected, pressure on both the high and low gauges stays at 90psi the whole time (clutch engaged or not), then 5-10 seconds later the clutch disengages and the AC light begins flashing.

Anyone seen this before and/or know what the problem is???

nthach

You got a blockage somewhere or the compressor might be shot due use of a "death charge" or bad reed valves.

LScowboyLS

are you SURE the inside part is turning (the compressor) - even a worn out compressor should move the gauges a little bit


correct - your Nippon Denso 10PA20 is not that type


sounds like a good assumption

not with a broken shaft

cool!

even if you had inadvertently hooked your gauges up to two high side ports or two low side ports at once, the pressures would be the same, but either lower or higher than 90

PS - a "blockage" as someone mentioned would not give this result, but instead, both pressures would be weird, such as low side way too low, and high side way too low as well, for example

I would try a Denso compressor from a reputable source, RockAuto has NEW ones for only $290

PS - the correct way to do this after a compressor failure is to replace the dryer, and the expansion valve and flush the system with Kwik-Solv using compressed air and a flush gun

however, I agree with your logic here, I would also want to see the system working at least decently with a junkyard compressor, before going to all of the trouble above to fix it correctly, just in case it is some weird problem in the A/C logic board or similar issue.

I am an ex-A/C specialist for the largest Lexus dealership in the world - JM Lexus, Margate, FL

zukikat

Great feedback man, thanks!!!

So it really sounds like my suspicions are correct that this genuine Toyota/Denso used junkyard compressor has internal issues even though the junkyard car it came off of had lots of freon (spewed freon for quite a while) until we opened its' system to remove the compressor.

I checked for freon and then rocked the clutch disc by hand to make sure it wasn't seized when we decided to pull that compressor in the junkyard but I didn't think to turn the front clutch disc by hand and listen/feel for piston stroke sounds once the lines were off before we pulled it from the junkyard car and now I'm wishing I'd tried that before we installed it...

Just to ask, are there any known LS400 ECM gremlins anyone's seen before that could be causing this car's current a/c symptoms at all?
I wouldn't think so as the hi/lo pressures don't change from static pressure on clutch engagement and the climate panel diagnostics say 00 for codes, but after all it "is" a Gen 1 LS so of course I have to ask...

Exactly... That's the plan. Junkyard compressor to test the system first...
I don't always do the expansion valve as they're not always accessible without dismantling a large portion of a car's dash/interior and usually aren't faulty on a system that still had a charge on it unless there was contamination but the drier is always a must once I've opened a system for any reason or if the system was leaky to a point where it lost its' charge on its' own...
We didn't do the drier (yet) because it was sunday, we'd just finished a 1UZ timing belt/water pump job on the car at 2AM the night before, and none of the parts stores that had a drier in stock for an LS were still open so I decided to try to at least charge the system just to make sure it runs and gets cold at all, figuring I'd do it right and replace the drier next weekend if it worked and successfully held the charge all week.

Best laid plans, 'eh?

My thinking is that if both lines of the gauge set were on the high side or both on the low side they'd both read the same but there would still be a matching change on both gauges to the low or high pressure whenever the clutch engaged, although if everything were working properly and I'd mistakenly used two high side fittings the low side gauge would probably break from greatly exceeding its' scale. Is that a reasonable assumption?

Can anyone post a pic of the two valves at the firewall on the Gen 1 LS400 and mark in the photo which one is the correct one to use for charging the system?
Or does it matter which one gets used as the low side fitting for charging the system?
I assume there's more than one for a reason?

LScowboyLS

there absolutely is!

the most common ECU gremlin of all, failing ECU capacitors can cause the compressor to not come on

as you may well know, the ECU controls compressor operation in the LS400

however, if this were the problem, the clutch would not engage, it would be as if you had pulled the power to the compressor coil



here is a much more foolproof way, and once you learn, you will be able to answer this question on any car you are looking under the hood of

learn how the A/C system actually functions, and trace the circular route of the freon, and you will always know whether a port is high or low pressure, by its location!

the freon is at high pressure as it leaves the compressor and remains at high pressure through the dryer, the condenser, through the small diameter all-metal "liquid line" all the way to the expansion valve under the dash, and at that point is changed to low pressure, and stays low pressure in the evaporator and the through the larger diameter suction line all the way back to the compressor to begin the cycle again.

zukikat

Thanks again for your help so far!

I'm hoping to get a chance to take a closer look at the compressor over this weekend, maybe disconnect the lines and turn the clutch disc by hand and see if I can determine if it's actually turning the shaft internally when the clutch disc is turning or not.

We may also try looking at the junkyard for another compressor but the yard is about an hour's drive away and it's a holiday weekend with lunatic drivers and lots of law enforcement out in full force already.

Once I get a chance to check it closer I'll post my findings.

LScowboyLS

Lexus/Toyota (NipponDenso) A/C is the most reliable A/C system in the world, and I have worked on all of them for over 35 years, so it's a good investment, just don't cut corners and stick with the Denso parts

mglawrence

Hey what did u ever find out? I'm having the exact same problem and my compressor is BRAND NEW! Comes on for five seconds then shuts off. Please help! My readings on the gauges are all messed up too just like yours. If I keep pressing the ac button back to back I can keep the compressor running and I get ice cold air. Or if my rpms stay over 2000 the ac light will stay on and I get ice cold air. But otherwise, whenever I turn on the ac, the compressor kicks on, then, 5 seconds later, the ac light starts flashing and the compressor kicks back off.

dicer

Do a search on youtube, I tried but at this time nothing seems to work.

fixmiester

Classic symptoms of too little freon in your system ; you probably have a leak somewhere, (when the compressor was installed?). Find and fix the leak first, then charge the system. The on/ off cycling is normal during recharge, unless you bypass the low-pressure switch, which speeds up the process considerably.

mglawrence

Hey. I should have mentioned I evacuated the system and recharged to 2.42 pounds. Also I did a pressure test and there are no leaks so that is not it. Any other suggestions?

dicer

It could be lots of things. There is a pressure switch that lets the system know there is pressure. Could be the new pump. There is a diagnostic check, the system will self check, I don't have time to type it up now. And my info is for 92 and likely works on 90 to 92 since the control display is different for 94 I'm not sure if the diagnostics works the same.
There are sensors, and things like the expansion valve etc. pressures is more like something going on with the basic system.

fixmiester

If your old compressor failed and spewed debris into your plumbing, you must clean it out, not just evacuate and recharge. Usually requires a new dryer and at least a cleaning of the expansion valve. Not easy, but important.