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92 Ls400 Ac Problem


wags70ss
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Hello, new to this forum. I have a 1992 LS400. I have owned it for several years. It is the second one I have owned.

I am a master mechanic with over 35 years of expirence. I have always worked on all my own cars. I replaced the engine in my first LS (that was fun!)

& have done extensive work on this one too.

Here is my issue. I replaced the AC evaporator last year & all the seals in the system. I converted it to 134a & it worked great. This year when I went to use it the first time, it did not blow cold. I have checked the freon level & it is OK, & I have run the diagnostic on the LCD & get a 00 code, but it does not blow cold air.

Has anyone expirenced this issue or can anyone tell me what may be the problem? :chairshot:

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Is the compressor running? Is the AC clutch engaging? There is some pressure safety valve in the system to prevent the compressor from running if freon is too low. Or it could just be the solenoid windings are blown. Either way I'd confirm compressor and clutch before spending much time on other things.

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Yes everything is working the way it should. Compressor is running, climate control is working properly, no codes, inside temp sensor is plugged in (removed panel under the column to check it), heat valve arm on the fire wall is moving when I move the temp from hot to cold. It should work, but its not. Thats why I am stumped.

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I checked the heat valve & appears to be working normally. The top hose is hot & the bottom hose is cooler. When I turn it on hot, they both get hot.

Engine temperature is normal, but I noticed that even with the ac on, niether of the fans are running. Its only 66 degrees here today, so that may be why.

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One other note: I rebuilt the front end over the last couple weeks & also replaced the radiator. I noticed that there is a sensor at the bottom driver side of the radiator. Does it have anything to do with the ac system?

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Well if the refrigeration system is working properly then it has to be the routing of the airflow. Perhaps the heater core is still hot and preheating air before as it passes through the evaporator. There is an electric heating element on the newer versions of these cars for warm up before the engine coolant heats up. Maybe yours is stuck on.

If refrigerant is low the evaporator core can ice up. Then air doesn't get through. This takes some time to happen though so would not be noticed immediately. Anyway to get one of the infrared temperature guns ( http://www.harborfreight.com/non-contact-laser-thermometer-96451.html )and point it to the evaporator core while running. It should be 20 degrees cooler than ambient.

My guess is that some of the air routing flaps are either stuck or in the wrong position, dampers not working, linkages disconnected, and not routing airflow through the evaporator core. This assumes th refrigerant system is working and properly charged with refrigerant.

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And if you put gauges on the high and low side of the system, what kind of readings do you get? Perhaps the evaporator nozzle is plugged? Gauge readings may reveal what is going on.

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Yes everything is working the way it should. Compressor is running, climate control is working properly, no codes, inside temp sensor is plugged in (removed panel under the column to check it), heat valve arm on the fire wall is moving when I move the temp from hot to cold. It should work, but its not. Thats why I am stumped.

I'm betting the compressor is NOT running.

Look closer while someone else turns it on and off.

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