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97 Lx450 Cooling, Temperature & A/c


Thi
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Summer is comming and my 97 LX 450's cooling system could be better. After a good highway cruising with some passengers in the car, if I pull off to some side road, the temperature climbs a little bit, and the A/C cuts out. If you have a 450, does your car behave the same? Does the A/C stay on all the time (well beside normal A/C clutch cycle)? The A/C works fine when the ambient temperature is below 90 degrees.

The thermostat on my truck was replaced last year & the system was flush also.

With the later model LX470, Lexus equipped them with electric fan. If you know some after market solution for better cooling, please let me know.

I'm open to any suggestion. Thanks.

Thi

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The truck didn't have these problems when it was new. So factory original engineering is not at fault. Therefore the solution is determing how the truck was altered from factory original mechanical condition and correcting these alterations. "Alterations" including the use of anything aftermarket in the truck since it was new (thermostat, antifreeze, tune up parts, tune up specs, etc.)

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I agree with you. If I put on an electric fan, that's just a bandaid solution which does not solve the real problem. I bought the truck used so I don't know its original characteristic. It would be ideal if I can find someone with a 97 LX 450 & datalogger so I can compare the data & have some reference point.

Thi

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Sounds like a possible problem with the radiator. Have a friend who got a bunch of mud on his radiator -- caused his rig to overheat just as you describe. Had probs with the A/C too.

The symptoms you describe do not seem normal. The AC should stay on until you reach your desired internal temp (assuming you're using the Auto temp control), or blow cold the entire time.

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Thanks Doug for the suggestion. I checked the outside & inside of the radiator and it looks clean. The temperature is usually pointed to the middle of the scale. When under load & not enough air flow, it rises a little above the middle level; then the A/C goes off. It seems like it anyway.

I looked in the manual and found a coolant sensor cut off switch. As I remember, it is shorted when the temperature goes above 226 F. It's opened when the temperature gets below ~180 F. The A/C uses several parameters in order to turn off the A/C clutch; that's one of them. As I understood, the A/C will stop if the switch is shorted.

They show another coolant sensor somewhere inside the cabin. It's hard to determine the exact location from the pictorial drawing. From what I can gather, it may be located somewhere on the passenger side. In the past, the truck had problem with water leaking in the passensger side.

I wish that there's a data port for each major component such as A/C, transmission, emission,... If the input parameters for a given component is easily monitored, that would make debugging problem easier. ODBII port provides some information, but not enough and pretty generic sometimes.

I start to use the datalogger again in order to track the characteristic of temperature vs. A/C cycle.

If you run across some others clues, please let me know. Thanks.

Thi

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Thi, I still bet it is the radiator. Mine has been replaced (along with most other things on this truck) and it runs the same in hot weather or cold. Even if the water is flowing, it could be plugged up some and cause your symtoms

If the water temp turns out to be "normal" than it may be something in the A/C. I had a ford truck that did something similar to your description and it turned out to be a bad evaporator.

Just my 2 cents.

Good luck.

Andrew

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Thanks Andrew. I'll check/monitor the coolant temperature more closely.

I brought it to a local Lexus one time and they was not 100% sure of what's the cause. It's an intermittent problem so it was hard for them to debug also. One theory was the evaporator valve is frozen; but when the outside temperature is around 85+ or in the evening, the A/C seems to work OK. I would think that if it's frozen than it would happend in those instances also. However, I will look ino the evaporator valve, & receiver drier side also.

Hope your truck is running better now.

Thi

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You could be chasing several seperate faults here, #1- I beleive that if the Lexus LX450 AC system is low on freon it will work effectively at low tempreature buy cut out when it is unable to provide effective cooling at higher tempreatures #2 It is possible your cooling fan clutch is not working correctly? does the tempreature rise when travelling in heavy traffic? #3The auto climate control relies on several sensors to operate if 1 fails it may have tjhe effect you are experiencing.

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Ellioh,

A Lexus dealer checked the Freon and fan clutch before. The car does not overheat in heavy traffic. After a long highway cruising, if I get off to a smaller road, sometimes the temperature gets above the middle mark a little. That's when the AC cuts off. Thanks.

Alaska_LX,

I will get a tool or have someone pressure test the radiator. Thanks.

Thi

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