Bob99b5

The AC on our '04 RX330 has started acting up. Refrigerant level is fine. When the system works it's ice cold. It'll run more often than not, but occasionally the AC compressor just won't kick on. I searched the forum and found issues in other toyotas and lexus models with the magnetic clutch relay but for the life of me I can't find where that is on the RX. I also saw refernce to an AC "servo" in another thread. Any ideas of what controls the AC compressor and what to check?

lexus114

Does the A/C light flash when it acts up? Could be a temp. sensor too.

Bob99b5

No flashing A/C light. Today it ran absolutely fine for 45 minutes, then started blowing warm, then "fixed" itself again!

HtownBlue

My A/C had interment issues last summer. Turned out that one of the cooling fans had a bad connection with the wiring harness and the AC would only work when moving.

Check that your fans are working properly. Also check for pressure levels in the a/C system. You could have slight obstruction in the system usually caused
From dryer bits breaking loose. Watch to see if clutch is indeed engaged when the issue happens.

HtownBlue

Another post:
The Clutch Relay is located in the fuse box under the hood.
The Magnetic Clutch is within the compressor itself.

Check the A/C Relay sometimes known as Clutch Relay in the fuse box area.

As for the servo: this is the small electrical motor that switches the "path" of where the air flow will be directed (vents, defrost, lower vents, combo, etc). Sometimes when this goes out, you cannot get air directed to the proper vent outlet on the vehicle.
The servo though would not cause sudden heating of cold air in most cases though. Unless it directed the air flow to the heater coil, I would not think this is the issue, but I wouldn't count it out as a possibility. - try switching to max heat when the AC "acts up" then switch back to max ac.

Bob99b5

Thanks for the tips, I'll check them out. For the life of me though I can't find this magnetic clutch relay anywhere. I found one relay in the small box over the passenger wheel - there were two in there, one labeled DRL (which disabled the DRL's (duh!) when I removed it) and one labeled heater. When I removed that one, the ventilation fan stopped working but the AC clutch still engaged and disengaged when the AC button was pressed. So....it looks like that one doesn't control the AC clutch. A mechanic friend of mine looked it up on alldata and he says it's supposedly in the fuse box over the driver's wheel. I've checked that box three times now and can't find anything labeled anything like Mag Cltch. There was a 50 amp heater fuse but that one also just disabled the ventilation fan.

No closer to a solution yet but I'm not giving up. My brother owns a bodyshop and has alldata so I just need to get there and read all the troubleshooting procedures and find where the sensors, fuses, and relays are located and what they control.

But keep the ideas flowing...I really want to solve this!

HtownBlue

I'll find it tomorrow and post a pic for you friend.

Bob99b5

I think I'm getting closer on the diagnosis. I'm thinking now that it's related to engine temp and the cooling fan. Tonight I was leaving concert and idling in traffic in the parking garage for about 20 minutes. After about 15 minutes, the AC quit and I noticed the temp gauge rising. I opened the hood to see if the cooling fan was running but it was too dark to see (but I didn't hear it running and I don't think it was). After we got out of the garage and got some air flowing across the radiator, the engine temp dropped and the AC came back on and stayed on for the 1 hour highway ride home. I'm wondering if the engine cooling fan isn't come on properly, and if there's a fail safe mode that disengages the AC when the engine temp rises about a predetermined set point?

Dave Mac

I think you about have it figured out. I had a car a few years ago that acted just like that and it was one of the electric fans not coming on when the temp went up and that in turn caused the AC to stop cooling properly. I tried replacing the relay which should have solved the problem but didn't so since it was about the end of summer I just nursed it along - hard to do in Arizona - and traded the car in the winter. All I usually had to do to get cold air flowing was get out of the parking lot or whatever and gain a little speed. I was a little frustrated that I never could really pin down the problem but when the relay didn't take care of it the next component was a very costly module I believe.

Good luck with yours.

Dave Mac

lexus114

These things actually have some kind of computer module that controls the fans (if I`m not mistaken)

HtownBlue

Again, read my above post friend. I had the same issue. The problem is likely not the fan motor, NOR the fan control module, as I replaced both without resolving the problem. After several attempts of resolving the issue, we discovered it WAS THE CONNECTION FROM THE AUXILLARY FAN TO THE CONTROL MODULE. We found the connection wires were loosely connected. We carefully took apart the plastic connectors, and used pliers to re-establish good connection between the metal prongs and the wire itself.

Please try this before hand friend. Save yourself 600 dollars in parts firt and try repairing that fan motor connectors.

I had the exact same issue an this solved it for me.

HtownBlue

At high engine temp without the fan pulling cool air over the condenser, the condenser cannot do it's job. The engine temp does not directly cause AC clutch to disengage, it is the lack of air flow over the condenser that is the primary issue. Without the air flow, there cannot be the needed heat exchange.

Bob99b5

My AC issue turned out to be a leaking radiator, a known problem on the 2004s. The car would run hot, but not boil over, and the logic in the AC system would shut down the compressor to help cool the engine. My dealer replaced the radiator and coolant free of charge for the second time (1st time was at 1 year old). It's been fine since. I had previously verified that the fans were cycling properly so I never tried tightening the connections.

Thanks to everyone here for all the advice!

Carver

Bob, does your car have the towing package, HD rad, HD alt and larger trans cooler?

Bob99b5

not sure on the alt, but from what i remember it has all the rest.