Need advice: airconditioning problem

[kathleenkmh]

My a/c started blowing warm air during a long distance trip. I took it to a heat/aircondition shop. This was the outcome: "Inspect pressure and found that system has enough freon to engage the compressor but it will not. We have inspected for codes, Code 21 store (solar sensor). Inspected fuses they were okay. Cleared code, but it reset right away. We have checked AC relay and have found that it will supply voltage to AC for approx 2 seconds, then will turn off. System will shut down power to AC clutch if it does not get an ac compressor RPM signal"

Now...the solution to this (I was just faxed the estimate) is to remove and replace the AC compressor and AC relay. The compressor is $884 (parts) and the relay is $110. I am not a mechanic, so I have no way to assess this, but it seems to me that the problem is in the AC relay... why would the whole compressor need to be replaced? Any advice/explanation would be helpful. Thank you.

[AWJ]

Sorry to hear this. My AC is not cold. I suspect it may be the same issue, but I have not checked up on it. I would try the relay first. I'm sure they can be found cheaper. Check e-bay or there are some other sites too. I'll get them.

Either way, let us know what you find out please.

This may be handy:

http://www.used-car-parts-exchange.com/cgi...ml?l_make=lexus

[pauldridge]

there are a number of conditions which will cause the AC ECU to turn off power to the compressor clutch... high drag on the compressor, inadequate freon pressure, etc. If not already, I'd at least take it to a Lexus dealer for final opinion before springing for the new compressor. I had a solar-sensor check code, along with several others, turned out, in my case, the speed sensor info was not getting to the ECU. There never was a solar-sensor problem!

[Rave]

Paul

So from your message I gather the solution was to simply replace the engine speed sensor module? Or was there some other problem? I have had this problem (speed sensor failure) in other vehicles but it usually manifests itself as engine stalling at idle, and cruise control won't work etc. I'm not sure how this would show up on an SC. My air conditioning failure sounds like the problem in the original post in this forum. AC worked fine on cool days and works OK when first turned on. On a warmer day the AC progressively fails and after 15-20 minutes of driving puts out no cool air at all. The next day when I had a chance to check it out the freon pressure was fine. However on a cool evening with sunroof and windows open and AC on max cool the compressor clutch would engage for a second or 2 and then cut out. You can clearly hear this without even opening the hood. The compressor clutch makes a substantial click when it engages and the engine idle RPM increases about 500(from 750 or so to 1250 or so). Is this a systematic problem with these cars?

[Rave]

I had some luck working on above problem with my A/C. Compressor would not stay engaged. Only warm air would blow after the first 2-5 minutes of operation. Traced problem to the high pressure switch. A/C system has a switch on the high pressure side just before it goes into the firewall to the evaporator. Switch is near the top of the passenger side shock absorber tower. You can hear it cycle on and off as a very faint click about 1/2 second before the A/C clutch engages. If you put your hand on the switch you can feel it toggle from on to off. I jumpered this out and within seconds fired the pressure relief valve and some of my freon blew off. After this system works fine and blows cold. I think the system was overcharged and caused the high pressure switch to deactivate the compressor all the time. Funny thing is my fill gauge which only looks at the "low" side pressure was right on spec. I needed to look at the high side pressure but din't have the tools. This week should be a good test. We are expecting temps in the 90's every day. I hope it keeps working.

Stay cool evereybody.

Rave

[Rave]

Works like a charm. Presure on low side of system is at min per my cheap gauge but A/C seems to work fine. Compressor works fine and stays engaged-air blows cold!

Rave

[TomTA]

Can someone please tell me where the air conditioning relay is located? I need to start looking for the reason I don't hear the compressor clutch kicking in. At least I think I should be able to hear the clutch engage. Thanx in advance. Tom