New AC and having problems

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    James Culbertson
    James Culbertson

    Hello. I recently replaced my entire AC system on my 2003 Toyota Tacoma. It’s had a number of issues over the years so I just decided to replace it all myself after the 3rd compressor in as many years decided to lock up. The shop that did the work offered warranty to replace the compressor and condenser but would charge $800 for labor. Ouch!

    New compressor, condenser, drier, evaporator, and expansion valve. On the compressor/condenser/drier, I was able to source the OEM parts from Denso. The others had to come from UAC or ACDelco (expansion valve). So I got everything installed without too much trouble after having a local shop evac the system. Toyota calls for 7.75 oz of oil in the system. The Denso compressor comes with 3.4oz in it. On the advice of Denso, they recommended starting up with only 2oz in the compressor so I removed 1.4oz and distributed it across the evaporator, condenser, and drier. Additional oil was put into those three components to get to the 7.75 oz for the total system usage. Anyway, I vacuumed the system. I’m at approx. 5400′ ASL so couldn’t get much better than 22-23InHg on the vacuum. I have a moisture detecting sight glass that seemed to indicate I was good when I stopped the vacuum to charge (about an hour of vacuuming after leak checking and oh, we are currently at 9% humidity here…need rain badly!). Charged up with 1-12oz can of R-134A as vapor on the low side. System pressure went to about 70psi. At that point, I started the vehicle and turned on the AC. Compressor turned on and I proceeded to add nearly another can (11oz) to get it to Toyota’s spec of 23oz. Fed it in as vapor on the low side. I noticed that the low side was not dropping pressure and my compressor is not cycling. Ultimately when I got all 23oz in, the low side qas was quite high (I don’t recall the exact number but I want to say about 150psi). The High side seemed normal at around 225psi given I was working in a pretty warm garage. By the time the refrigerant was in, the running of the truck had heated things up to about 95F in there. So at that point, I shut it all down and called it a night. The next day, I checked static pressures and they don’t match between high/low side. I ran the system and the compressor is turning and I get great cool air for a while then things start going warm. The low side never drops pressure while the compressor is running and my compressor is not cycling like I would expect it to. I shut it all back down to do some investigation. I did a resistance check on my Thermistor and it seems to be working but I cannot find any details on expected resistance values/temperature so it could very well still be bad. I do know that when I disconnect it, the compressor shuts off. My pressure switch seems to test out ok as well showing the switch is closed at the pressures currently in the system. I should add that my fan clutch has probably seen better days so I may very well not be getting the air I need across the condenser. I’ll get that changed out but I don’t think it will improve things tremendously.

    The low side is reading 97psi this morning (garage is showing at ~80F) and the high side is reading ~135psi which seems a bit strange that they aren’t equalized. What has me baffled is when the vehicle runs, the low side doesn’t drop and I’m not getting any cycling of the compressor and even if I manually shut off the compressor, the low side doesn’t change. So I’m thinking a few possibilities.
    1. Compressor is bad. I really hope this isn’t the case as it was a brand new OEM compressor. It’s quiet, belt is well tensioned, and when I manually spin it, it feels smooth.
    2. Thermistor is bad. This might explain why things are not cycling.
    3. A problem with my expansion valve. The exp valve seems to me anyway, to be leading culprit as I’m thinking it may be partially stuck and not regulating as it should.
    4. Another possibility which I hope isn’t the case is the AC Control module–$$$

    So unfortunately, I will probably have to get the system evacuated again and dig back into it. I was hoping someone with more experience on these systems might be able to offer me some advice before I start throwing parts at it. It’s hard for me to believe a new compressor or expansion valve have failed (I didn’t change out the Thermistor but will if I have to open it all back up….it’s cheap) but I know these things happen.

    Sorry for the novel. Thank you in advance for any advice you may have.

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