HVAC blower shuts off when on high... and now A/C doesn't work.

[AceFrehley03]

Starting to have HVAC issues with my 2005 Infiniti QX56 and it's making me wonder if I have multiple issues or just one.

Last year, the blower motor resistor/controller failed (only off or high) so I replaced it with a new module. The existing resistor (which was original) was five fin, the new one that went in was four fin. Seemed to work fine. Now that it's getting hot, when I go to run the fan on high or auto, it will run full speed for at most two seconds and then click off. The display will still show is as full or auto. If I turn the fan all the way off it will reset and let me turn the fan back on again. I can run any speed reliably except for full. A few weeks later (week before last), the A/C failed. The compressor clutch isn't engaging, it isn't trying at all. I put a manifold on the compressor lines and there's some residual pressure but it is low. It's also hard to say how much R134A is in the system if it sprung a leak somewhere, which I'm really hoping not.

I'm starting to wonder if it's the HVAC controller which has failed and these two issues are related. The rub is that this part is no longer available from Nissan or Infiniti and they're rare as hen's teeth at wrecking yards.

To try to check, I hooked up my MX808BT and read live data and the scanner does show when A/C is engaged, which I THINK is proof that the HVAC controller is at least trying to command the clutch to engage on the A/C compressor.

Has anyone encountered one or both of these issues before?

EDIT: Forgot to mention, no CEL and no codes. Onboard diagnostic came back with nothing.

[VStar650CL]

If it's blowing up resistors (actually VBC's, it's a MOSFET transistor with a giant heat sink), it almost certainly means your blower motor is going south. It should have been replaced along with the first VBC, you never replace a VBC by itself. If a motor goes bad but the VBC is good, you can replace just the motor. The reverse is untrue, when a VBC fails it's almost always because the motor is drawing too much startup current and gradually killing the MOSFET. So you replace both, even if the motor seems to be okay. Chances are it isn't.

Regarding the A/C, the ECM positively won't let the compressor engage if the refrigerant pressure is too low. So you won't know anything else until you get it leak-checked and recharged.

[AceFrehley03]

I found a random can of R134A in the garage so decided to put a bit in and wouldn't you know it, the compressor kicked on. Now I'm chasing a leak. Hurray.

[AceFrehley03]

If it's blowing up resistors (actually VBC's, it's a MOSFET transistor with a giant heat sink), it almost certainly means your blower motor is going south. It should have been replaced along with the first VBC, you never replace a VBC by itself. If a motor goes bad but the VBC is good, you can replace just the motor. The reverse is untrue, when a VBC fails it's almost always because the motor is drawing too much startup current and gradually killing the MOSFET. So you replace both, even if the motor seems to be okay. Chances are it isn't.

Regarding the A/C, the ECM positively won't let the compressor engage if the refrigerant pressure is too low. So you won't know anything else until you get it leak-checked and recharged.

Should’ve clarified, both resistor and blower have been replaced. No change.

[VStar650CL]

Should’ve clarified, both resistor and blower have been replaced. No change.

Well, the blower shouldn't care if the compressor is working or not, and it certainly shouldn't be shutting down after 2 seconds of run time. Put a voltmeter on the wire connecting the blower to the VBC. If the voltage goes to near zero when the blower stops then the problem is in the motor or the blower relay, if it goes to near battery voltage then the problem is in the VBC or control circuit.