Automotive Air Conditioning Information Forum

I see your thought.

I may not have been clear either. The evap isn’t a constant 39*. The clutch is in a constant state of cycling. So the evap temp cycles from 39-47*F
There is no constant “running temp” vent temps are anywhere from 48-58 during this process. Idling the engine at 1500-2000 rpm actually makes the temps higher, as the effective “clutch on” dwell time is reduced.

It appears to me that the TXV just isn't working right for some reason. Is the sensing bulb making good metal-to-metal contact with the tube, and Is the interface of the bulb and tube well insulated with Prestite™? Is the equalizer tube hooked up, and is the fitting snug? The temperature differential between the evaporator core and vent temperature seems off, though. Not too much remaining that I can point to other than the cool-ish ambient temperature.

Yes, the evap pipe had an indention for the TXV to cradle and I used the OEM metal attach clip and insulated with 1/8 adhesive backed neoprene closed cell aviation foam. All lines were secure and no kinks.

As mentioned I tested the TXV I replaced and could see no movement of the needle what so ever. I removed the hollow allen screw from the valve and removed the spring and needle seat. Using a small needle nose I was unable to move the needle at all.

I ordered an OEM expansion valve from the dealer. There are 4 in captivity in the US, so it’s coming from Florida. Be here next week.

Mark86 wrote: ↑Thu Mar 02, 2023 10:16 am I ordered an OEM expansion valve from the dealer. There are 4 in captivity in the US, so it’s coming from Florida. Be here next week.

Good deal. Hopefully, that'll fix it.

Received the new OEM TXV from Mitsubishi. Attempted to bench test it and it shows no needle movement at all. Used my hand and a cup of crushed ice and water to heat/cool the sensing bulb. Used a sharpie to put a small red dot on the center of the needle. There is no apparent movement of the the needle. Blowing through it is a very subjective test but in doing so it yielded no change in perceivable airflow.

Compared to the removed TXV using mouth air, it flows significantly more air.

How much movement should the needle have? .001” .010” etc.

Is anyone familiar with a facility that could accurately test this in the Phoenix area?

If you haven't already tried, tightly seal the end of the equalizer tube or pressurize it and retest. I've never done this, but I think the needle should move ever so slightly between the temperature extremes. It'll be hard to see, but I'm guessing maybe 0.030" at most.

If needle movement still isn't visible, I would install the new TXV, evacuate, recharge, and see how it performs.

The removed TXV might be stuck open, causing it to flow more air.

I don't know of a shop anywhere that's set up to test a TXV. Normally, it's just replaced if suspected of being bad.

John, I didn’t read your post prior to diving in to the Montero tonight. Good news is I can have the evap housing on my bench in about 20 min now.

Installed the new OEM TXV. So on my bench I have the unknown replacement TXV that was installed before I started this project, The TXV I installed and the new OEM TXV. Both of the non OEM valves move little air during a mouth test. The OEM moves more.

I installed the new OEM TXV tonight, vacuumed and charged. The results were better, but the problem persists. The dwell or “clutch on” time is better, it is still drawing down to the high teens on the LP side. It’s still starving for flow.

I didn’t pursue a collapsed hose, as that is downstream of my LP service port. EVAP—HARD LINE—-LP Serv Port—-Hard line—-Hose—- Hard line—-compressor. If I it was blocked, at the hose, the pressure should be normal prior to the blockage.

The HP liquid line from the R/D is all hard line, and the R/D is flooded (sight glass) when the comp is on.
(Maybe remove and air test again)

Before digging the exp valve back out, any thoughts? Wrong compressor? If my restriction is the Exp Valve there is an adjustment screw (hollow Allen) on the inlet. CCW to increase flow? CW to decrease flow?

I’m going to hook my gauges up and observe the system other than during a charging event.

"CCW to increase flow? CW to decrease flow?"

Correct. It doesn't take much...maybe 1/4 turn

Let's get a full set of pressures/ambient/etc

Pressures are a range. Clutch cycles on, low side goes from 45 to 18-19, which is better than before 14-15. The needle never stops, it moves slower the lower the pressure gets, but continues down until the Compressor cuts off, (low pressure switch I’m assuming). Then the LP side rises to about 45 and the compressor kicks on and the cycle repeats. The on off times are about the same.

High side is 140-170

Temp in my garage was 73.

HVAC fan pulling from outside cowl air which is essentially warm engine air.

Duct temp 50-58* constant up down with comp cycling.

Engine at 1500 rpm.

No moisture forming on any lines or out of evap drain hose.

In my mind, I keep going back to the TXV. At a 73°F ambient, the high-side condensing pressure seems excellent, but the erratic low side just isn't normal. The LS pressure shouldn't continuously drop and bump into the LPCO like that. If it's working correctly, the TXV should smoothly throttle the liquid refrigerant into the evaporator to keep the LS pressure at or near 30 PSI. You can adjust the superheat spring, but it's a nuisance because you have to recover/evacuate/recharge each time you do so.

I think I'd wait until the daily ambient temperatures rise into the 80°F range, retest, and see what you get. If no change, I'd first take another close look at the sensing bulb, ensuring that it and the pipe it contacts are clean, tightly clipped together (direct metal-to-metal contact), and well insulated with Prestite™, removing the insulating material you have on there now. Also make sure that the equalization tube isn't plugged and is snugged-up nice and tight to its corresponding fitting.

As a last resort, I'd consider adjusting the superheat spring in the TXV. But I really hate to do that since it's factory-set using sophisticated calibration equipment to which none of us has access.