Fairtax4me Posted November 6, 2015 Share Posted November 6, 2015 http://www.ultimatesubaru.org/forum/topic/152408-ac-clutch-wont-engage-96-legacy/ Down in the lower half of that page there are diagrams and some info on how to test the termal control amp. Basically, you're looking for a 12v signal going to the computer, ( the pin at the ECU will be different on your model than what's listed in that thread.) The 12v coming out of the thermal switch turns off, IIRC, when the core gets too cold. The amp circuit relies on some amount of resistance through the thermister. Resistance gets high when the core gets cold, which blocks current flow through the amp circuit, and thus switches the 12v signal off, and the ECU turns the compressor off. Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 6, 2015 Author Share Posted November 6, 2015 I was running the car on max cool for only about 5-8 minutes in 60 degree weather. Would the compressor not shutting off, in that limited amount of time, cause the white ice on the lines like it did? By the way - thanks for that great link and associated diagram. Think I should pay up for the Subaru Expansion Valve? I'm willing - if you think it makes sense. $90 vs $20..... Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 7, 2015 Share Posted November 7, 2015 Yeah. Cooler weather is where that temp sensor is really needed. Part of what keeps the core from freezing is the heat from outside air moving across the core and being absorbed by the core. On a hot day (90°) the core may maintain a constant 34° just because of the flow of hot air across it. But on a cooler day the core temp will be able to drop below 32° In a matter of just a few seconds. With the newer type expansion valves I've not heard or read of any problems with the aftermarket valves. That style is pretty common among a wide range of vehicles. How easy is it to remove the valve if it needs to be replaced again? Did you have to totally remove the evap core, or can the valve be unbolted and removed through the firewall? Pulling the core out is a big task on some cars, requiring total removal of the dash in order to get access. On a car like that, I'm going OEM because there's less risk of getting a faulty part. If the valve can be swapped in 20 minutes from under the hood, aftermarket would be fine. I'd also recommend replacing any o-rings that you can get to if you have the system open again. Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 8, 2015 Author Share Posted November 8, 2015 Getting to the evap core was a pain but I really wanted to see the entire circuit of the a/c system. When I finally got it out for cleaning I should have taken some photos but my hands were greasy. Unfortunately, I find my curiosity makes me rush to see the next thing. I should take before photos - because I always get hung up putting stuff back. An example was re-installing the spacer in the firewall. In the earlier photos - where I was trying to figure out how to disconnect the expansion valve (even though I had done it years before!). The rectangular opening in the firewall has a substantial rubber holder (gasket) that allows the metal spacer to sit on. The spacer - is what sits between the engine and the expansion valve - that serves as an anchor. When putting everything back - I couldn't figure out how best to position it. Finally got everything connected but I used to be able to hold a complete vacuum but this last time not quite. Anyway, the biggest gripe I have is the plastic, One gets frustrated and tempted to force things even though - you know it is the worst thing to do. Here is what I am getting at. I will buy the OEM parts - Thermister, Expansion Valve - figure out the o-rings and redo the whole thing......but what I thought I would do in the interim is understand more about the thermister. I can kick myself for not taking photos. If you visualize a blue plastic thermometer - narrow and about a half inch long attached to a piece of plastic - which gets inserted into a missing fin on the lower right quadrant of the evap core - that is the thermister. It has a thin insulated wire that enters 'behind' the harness in the picture. I can't see it but I assume the harness we can see receives a tiny harness from the thermister. I wanted to slide it out and disconnect because maybe I can do some testing on circuit but even if I can't test it - I'll need to be able to disconnect it when I put in the new thermister! But I can't figure out how to slide/pull/push or otherwise get it loose - I just know I am going to break this thing!!! Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 8, 2015 Author Share Posted November 8, 2015 The thermistor is actually in the lower left quadrant of my evap core. Core looks just like a mini-condenser. I re-inserted the plastic holder thermistor anchor in the empty fin with the sensor pointing up......again I should have taken a photo because maybe it was originally pointing down Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 9, 2015 Share Posted November 9, 2015 The dealer should sell that whole unit (thermister and amp circuit) as one piece. So you just unplug the orange connector and the rest gets replaced. Somehow or other that whole thing slides off of the white piece. Not a big deal if you break that, you can use a zip tie to secure it back. Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 9, 2015 Author Share Posted November 9, 2015 I can't budge that orange connector. It won't slide out. Quote Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted November 9, 2015 Share Posted November 9, 2015 (edited) it kinda looks like you should push it. If the cable is slack enough - worth a try. can you get your phone/camera or a mirror back there to take a pic? it might look different or show a tab or ???????? maybe visit a junkyard and practice on a wreck! Edited November 9, 2015 by 1 Lucky Texan Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 18, 2015 Author Share Posted November 18, 2015 Tex - you were right. I had to push it. Of course it still took me a couple of days to separate the brown harnesses Is there any point to trying to test the thermister harness (black) for resistance or anything. I'm still going to buy an OEM thermister and expansion valve from the dealer. I'm no electrical wiz but do have a multimeter. Just curious if it would verify anything? Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted November 18, 2015 Share Posted November 18, 2015 The only way you could test the temperature bulb itself would be to cut the wires and check resistance of the bulb. Might not tell you anything though. The little module there gets 12v in one wire (I forget which), another is ground, the third sends 12v to the ECU and that 12v gets interrupted when the temp bulb gets below freezing. If you can get 12v and ground to the correct pins, check the third for 12v with the bulb in open air. Then stick the thing in a freezer or really cold ice water and the 12v pin should drop to 0. Quote Link to comment Share on other sites More sharing options...
stackman1 Posted November 18, 2015 Author Share Posted November 18, 2015 The only way you could test the temperature bulb itself would be to cut the wires and check resistance of the bulb. Might not tell you anything though. The little module there gets 12v in one wire (I forget which), another is ground, the third sends 12v to the ECU and that 12v gets interrupted when the temp bulb gets below freezing. If you can get 12v and ground to the correct pins, check the third for 12v with the bulb in open air. Then stick the thing in a freezer or really cold ice water and the 12v pin should drop to 0. By the temperature bulb - I assume you mean the thermometer currently inserted into the evap core? Quote Link to comment Share on other sites More sharing options...
stackman1 Posted June 11, 2016 Author Share Posted June 11, 2016 (edited) I hope this link will work. I uploaded to youtube http://www.youtube.com/embed/rfHUDUuFFUY?rel=0 Edited June 11, 2016 by stackman1 Quote Link to comment Share on other sites More sharing options...
stackman1 Posted June 11, 2016 Author Share Posted June 11, 2016 Ok - looks like I did it. With any luck FairTax et all - still out there. I am about to take my annual trip to Florida for July (don't ask). To save you guys from reading the whole thread - 2 years ago the dealer told me the compressor was shot but through this board and its members I have been able to make the drive in comfort for two years running. Each June I have to work on it - likely due to leaks but have done quite a bit. I'll digress more later. It is in low 70's in NY. While the a/c cools now - not sure how it will operate in South Florida over the next six weeks. Yesterday after driving about 20 minutes with a/c on - I decided to video the a/c compressor. Can you guys tell me if that kind of cycling - in this kind of weather makes sense? Does clutch look right? More questions later - just quick opinion on the look of the a/c compressor operation. Thanks Peter Quote Link to comment Share on other sites More sharing options...
stackman1 Posted June 11, 2016 Author Share Posted June 11, 2016 FYI, I had subaru credits expering so I bought an OEM thermistor and Expansion Valve) but don't want to pull out the evap core again to replace thermistor. I did pull it out last year and cleaned it because of the icing. There was crud in the bottom of evap holder. Plus they never installed a blower filter. So ..... if compressor video looks ok to you guys. What should I see for readings on my gauges to know if I need to just 'add' R134a. I don't feel like vac'ing and re-charging completely if I can just add some. What the Low and Hi side numbers to look for - to tell me if I should just add some???? Thanks Pete Quote Link to comment Share on other sites More sharing options...
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