First timer, posting for first time. A while back my 2010 RX350's climate controlled A/C quit working about 2 months, and 1000 miles, after I replaced about 2 gallons of coolant. At about 130K miles I drained about 2 gallons of coolant from the radiator, front engine block drain, and the overflow tank; afterwards, I added 2 gallons of Toyota 50/50 coolant 00272-SLLC2 to the overflow tank and radiator, then I ran engine about 30 minutes to extract air bubbles. By the way, after the coolant replacement, the temperature gauge shows the needle going half way up the dial, which is the same spot the needle went to as before the coolant change; so, I believe the coolant change was done correctly. The RX350 now has 141K miles, and I've just realized both radiator fans NEVER turn ON even though the temperature gauge still shows the needle at its normal operating temperature position half way up the dial.

Back to A/C problem, no matter how cold I set the driver side or the passenger side, the temperature never gets colder than the outside temperature; however, the heat does work fine, and will heat to whatever temperature is set for the driver or passenger side. To turn on the A/C we have a button under the radio buttons labeled AUTO with a green light; when we press that button the green light comes ON, the FAN kicks starts blowing, and the button showing air recirculating turns its green light on too; but no matter what COLD temperature we set the driver or passenger side, the temperature coming out of the vents never gets COLD. By the way, I get the same results (no COLD A/C air) when I used the MENU button and joystick to go to use the navigation screen, select CLIMATE, to set the fan and A/C to try cooling the driver and passenger side vents to a cold temperature (ie. 66F).

I purchased a 20 ounce bottle of A/C Pro Ultra Synthetic A/C Recharge to see if the A/C system was low on R-134a refrigerant, however, when I hooked up the charging hose and gauge to the LOW pressure port, the needle on the gauge went into the RED section of its dial; the gauge goes from 0PSI to 150PSI, and the RED section shows it being from 60PSI to 150PSI; when I attached the hose and gauge to the LOW port, I estimate the needle went to about 100PSI; so, the gauge indicated there A/C system had something terribly wrong.

In the engine compartment I never see the compressor clutch spin, nor do I hear the radiator fan turn on. When I take the lids off the fuse box located in the engine compartment to expose the relays, and ask my wife to turn on the A/C using the AUTO button, I hear nothing from the MG/CLT relay, which I assumed stands for the A/C compressor's magnetic clutch, based on what I've read; however, I asked my wife to turn on the REAR defroster since there's a relay dedicated to that function, and I definitely hear the relay kick ON.

After reading a few forums I got the idea the relay labeled MG/CLT in the fuse box located in the engine compartment might be BAD keeping the A/C compressor clutch from spinning. The MG/CLT relay shows Relay Denso on one side, and Toyota 90987-02028 156700-329012V on the other side. Since the cheapest matching relay I could find online was $45, and my locat Toyota dealer wants $90, I went to my local salvage yard and pulled 2 identical relays from a couple of Camrys (older than 2010), since they were the only Toyota or Lexus vehicles with a matching relay. When I got home I swapped them out with my RX350's relay – neither relay fixed the problem. I realize all 3 relays (my original relay and the 2 salvage yard relays) could all be bad; regardless, I was hopeful if my RX350's relay was bad 1 of the 2 salvage relays would have worked.

1 l l 2
--- 3
–- 4

The MG/CLT relay has 4 blade looking pins. Using the diagram above as a reference of the socket the MG/CLT relay plugs into, with the RX350 engine NOT running, when I measured voltage between battery ground and pins 1 through 4 on the relay socket, I measured voltages in the millivolt range; with the RX350 engine ON and running I measured between battery ground and pins 1 through 4 on the relay socket again, and this time I measured in the millivolt range on pins 1 and 4, and measured 13.3 volts on pins 2 and 3.

So, I thought I should ask the RX350 – Gen 3 Forum a few questions. In the MG/CLT relay's 4-pin socket are there 2 pins I can short to emulate the relay in operation, in order to turn ON the compressor's clutch, to see if I can hook up the cable and gauge of the 20 ounce bottle of A/C Pro Ultra Synthetic A/C Recharge to see if the A/C system is low on R-134a refrigerant? Are there any board pins, or sensors, or cables, or other components, I can measure using my voltmeter to isolate where in the RX350's A/C system the problem may be? Are there any other “checks” I should do to further isolate where the problem may lie? What do I check to isolate why the 2 radiator fans are NOT turning ON?

 

I trust you checked your coolant level a few times after the change as it often requires additional topping a few days later.

Have you seen this older thread:
​​​​​​https://www.clublexus.com/forums/rx-...-solution.html