This is 3rd time happening. During a recent trip from ATL to CLT, the a/c stopped working. Fan was going, but no cool air. This happened on 2 other recent trips (within 6 months ownership of the RX) too. The crazy thing is it doesn't happen on ALL trips above 3 hours!
1sr trip to dealer they installed more R134a, 2nd trip they replaced discharge hose and clutch (tsb ac001-06).
The dealer now says the a/c clutch needs repositioning. Says the condenser(?) is freezing up and blocking the air passage......????
Any ideas??
Thanks

 

In humid weather the evaporator can freeze up, but the condenser? That's the coil hanging in front of the radiator.

The classic cause of a freeze up is low refrigerant. The evaporator will ice up if incoming air is very moist and the coil is too cold. Normally the expansion valve at the inlet of the evaporator will modulate the orifice, or in less sophisticated systems, cycle the compressor on and off to keep the evaporator coil from getting too cold, and allowing the ice to melt.

When your refrigerant (that R134a stuff) is low, part of the coil nearest the expansion valve will run very cold, forming ice - and because of the low system pressure, the compressor keeps pounding away trying to maintain what pressure it can, never cycling off and allowing the coil to thaw. Ice insulates the coil, blocks some of the warm air, and starts a cascade toward a total evaporator freeze-up. This situation can damage your compressor if not looked after.

In some cases, rare in an automotive system, the cabin air filter can become so clogged it blocks the passage of air, and leads to a freeze up. This is more common in a household system, but could happen, I suppose, in your Lexus. If your expansion valve is stuck, or the orifice is plugged up with some kind of foreign material, it can mimic this condition and produce a freeze up, requiring replacement, but a leak test can save a lot of money and is more likely to reveal a system leak as the culprit.

If you experience a freeze up, the quickest temporary solution is to shut off the compressor and raise the fan speed to circulate air over the evap. Set the system to "recirculate" to take advantage of the "dryer" air already in the cabin, and raise the thermostat setpoint so that the compressor goes off, but the air continues to circulate over the coil. Crank up the fan speed to "high". This will melt the ice in a few minutes and you can then lower the thermostat slowly to resume cooling. You may have to do this three or four times every hour, depending on the severity of the problem. At some point even this crude trick will not help much - your AC system doesn't have enough refrigerant to work with.

The basic problem is somewhere there is a chronic leak in the system that initiates this chain of events. I'm not sure that the clutch has anything to do with it, but is merely following its commands - kicking out on low pressure (insufficient refrigerant). That "repositioning" your service man refers to may be his convoluted way of expressing that.

If your dealer's shop isn't producing results for you, take it to another dealer. A good independent AC shop might get you a more knowledgeable serviceman, but won't honor your Lexus warranty. I'm no expert on any of this, but I spent years watching while holding wrenches and flashlights for my Dad who, ever the engineer - dissatisfied by available products - designed and built his own home and auto AC systems back in the day. I learned early on to greatly respect a good commercial product, a skilled service tech, and a good warranty.

 

Wow ... very nice post Lil4x

Salim

 

Hi, there was a tsb for sometype of connector freezing up or gettign wet from the sweat from the condensor. I believe the tsb called for replaceing this connector which came wrapped in some form of weather strip. It is an older tsb so im not sure if yours already has this. The way you describe it thats what the tsb fixed. call your dealer they can look it up and if they cant find it i may have some time monday at work to look it up.

 

Very good explanation Lil4x. One of the best I've seen detailing this issue. I'd suggest the OP take a printout of this to the dealer with him on his next visit.

 

Here is a brief recap of the invoice:
repl. cmpressor,w/mag clutch assbly overhaul
gasket kit
hub sub-assbly,mgnt
oil, cpressr

labor- cprssor not cycling due to incorrect clutch gap, causing evap to freeze up and popoff valve to refrgrt. Replaced clutch hub, set gap, recharge as needed.

I'll be taking a trip to Indiana in a few weeks, and will be monitoring this fix.

Thanks for everyone's comments.

 

I also agree, that A/C post was great!!