KhanBakki

I've been trying to tackle an issue with my A/C since out most recent heat wave hit just over a week ago. It was working just fine one day but blew nothing but hot air the next. My car is a 2004 with about 140k on it, no accidents, clean title, family owned and has been well maintained. I've been digging in the forums and have tried a number of tips and tricks (thank you everyone who contributes here!) but I'm running out of options and figured I'd try my own post before coughing up the dough to have it diagnosed at a shop. Here's where I'm at:

-Checked all fuses and relays that are at all related, even some odd ***** that were mentioned in previous posts.
-Visually verified that the condenser is not clogged up and both fans are functioning properly.
-Visually verified that the clutch on the compressor is engaging consistently when the A/C is turned on.
-Had a friend (professional at a shop) pull the refrigerant and verify the fluid and pressure are within range. It was a little bit low (I don't have records of the A/C ever being serviced) so we topped it off- no change.
-With the car off, we put power to the compressor which engaged the clutch, heavy resistance when we tried to hand-turn it (spun freely without power).
-Checked for signs of leakage- aside from being a little bit low, there was no grime, dirt or residue on the compressor or any of the lines. I understand that this is a closed system, so I assume there HAD to be at least a VERY small leak, possibly over the last decade, that would account for the lost fluid, but we didn't find signs of it. Fluid holding steady a week later.
-Ran diagnostics on the HVAC controls- came up '00'
-No blinking A/C light.
-No CEL.
-Unplugged battery for an hour, no change.
-Low side is not HOT, but not icy to the touch. High side seems to be warm.

It seems to me- and please, correct me if I'm wrong- that it's down to one of the following:
(a) debris clogging a line
(b) the TXV (not sure where it is or how to test it)
(c) this supposed "A/C Amplifier" that's been mentioned- looks like a controller behind the HVAC unit that does have control over the compressor, though I haven't seen the compressor NOT turn on when expected. Also- apparently these are incredibly expensive, so fingers crossed that a consistently working compressor is a sign that the amplifier is not to blame. If it comes down to it, I have seen a test I can run that requires removing the unit, but again, compressor kicks as expected.

Thanks for any ideas you folks can offer and apologies if I seem repetitive here, just want to make sure I'm thorough.

Bgw70

-Have you cycled the heat control hot to cold and felt a difference?
-what temp are you blowing from the vent vs outside air?
-do you see any bubbles in the sight glass when the compressor is running?

Expansion valve could be an issue.
https://www.buyautoparts.com/blog/ac...pansion-valve/

Bgw70

Your shop should be able to tell if the expansion valve (TXV) is the problem.

KhanBakki

Thanks for the reply!

-Very slight difference in temp between a setting of 65 and 85 degrees
-currently reading 74 outside, but I had readings of 107 last week, same results.
-no bubbles

interestingly, if I set temp to 85 when it’s 74 outside and I hit “auto,” it turns the A/C on. No clue what that implies.

VVTiBob

This thread..https://www.clublexus.com/forums/sc4...-then-hot.html
posts #6 and #8....wasn’t clear if you done this....or if you have a DTC reader and if you’ve had any code at the OBDII port?

KhanBakki

Yes, I followed the procedure, just wasn’t sure exactly what it’s called. Came up “00.” No OBDII codes either, and no check engine light. There doesn’t appear to be any computer system sending an alert of any sort (code, blinking lights, etc.)

Bgw70

Watch the video in post #3. Your HVAC shop can tell you what is wrong using the gauges.
the expansion valve is a big job for such a small part.

KhanBakki

The valve does look to be the most likely culprit after watching be video. I’ll bring it to the shop and see what the replacement really looks like in terms of time and money. Thank you for your help!

I’ll update this post accordingly, for the archives if nothing else.

Lexusdk

Did you verify if the ac servo motors were working? Maybe the servo motor is stuck on hot

KhanBakki

Afraid I must’ve missed that as a suspect- how can I verify it’s working properly?

Bgw70

Awesome question and what I wanted him to check when I asked him to cycle the control from hot to cold, back in Post#2 or see below.

see below.

I honestly don’t think this will be your problem because there are two actuators, they control hot/cold on each side, driver/passenger.
the passenger side hot/cold actuator is behind the glove box. Not difficult to access after the glovebox is removed.

https://www.clublexus.com/forums/sc4...from-dash.html
see post #9 for the hot/cold actuator repair.
see post#10 for the sound they make when they begin to go bad.
mine are still working great after I cleaned them up

MIGII

Change the a/c got mine from ebay $20 part.

Bgw70

The link you posted is for a VW and says it won’t fit an SC430

KhanBakki

Thanks for jumping in here- it sounds like the solenoid could be a valid culprit as well. Did your system throw any sort of code or indication that it detected a failure or error? Was the compressor turning on and off as expected?

KhanBakki

I'm using this article to try to get a better understanding of how the Control Solenoid works: https://www.motor.com/magazine-summa...t-compressors/

It's a bit over my head, but I'm really trying to establish a way to pin down the more likely issue between the solenoid and the expansion valve; I don't think the Low side line is as cold as it's supposed to be (very close to ambient temperature), and it seems that both parts could affect the flow of refrigerant. If I can't draw a clear line based on the evidence, I guess I COULD have a shop replace both parts when they drain the system, but I'm really trying to be as economical as possible.