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Discussion Starter #1
I've been having issues with my AC for a while now. Its a MCC setup. It cools fine, but cuts out after 30 minutes or so. I turn the heater knob up a bit thinking the evap has frozen. A few minutes later, the system will kick back on.

The fans work fine. I wired up an external set of resistors in parallel and have had zero issues. I've started to notice a thin layer of film on the inside of the windshield. It could be PAG or it could be coolant, I'm not entirely sure. I do lose a bit of coolant occasionally, but it takes 1 or 2 months before SID gives notice. There is zero residue on the drain snorkel.

I've been wondering what my AC pressures might be while driving, so I decided to hook up my Tech2 on the drive to work. I didn't have too much time to poke around, but I did access the DICE and the only thing I found was the EVAP Temp Sensor. The car had been sitting in my garage all night, I started the car and the AC compressor was off. Ambient was 71°F and the evap was showing 55°F. I kicked the compressor on and the evap dropped to somewhere around 6°F. This is certainly cold enough to make ice.

Is temp of 55°F on the evap normal when off? Should it have been reading closer to ambient? Where in the Tech2 menu can I find the high and low side or even the compressor sensors so that I can monitor their input? I couldn't find anything else related to AC system in the DICE menu.
 

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I don't believe there is any system diagnostic information on the bus... I think you need a set of manifold gauges to test AC system performance.
 

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Discussion Starter #3
I went out on my lunch break and did some poking around. I did find a menu for A/C inputs. There is no low pressure sensor, but there is a high side pressure sensor. When holding idle around 2k rpm the pressure slowly and continually kept creeping up. It is very warm outside and I was stationary. The fans were working as intended, but I shut the car off when the high side pressure reached 22.0 kpa (320psi). I must have a blockage in the system somewhere.

Earlier this spring, I replaced the high pressure line from the compressor to the condenser. While doing this I replaced the drier and the TXV. When I had everything apart I flushed the system with a cleaner. I added proper oil and amount and buttoned it up. My only thought now is that there's a blockage in the system. But how do I find it?

 

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That makes sense... there is an overpressure sensor, so it checks out its logged somewhere.

There is a trick for finding blockages... but I don't know what it is. :) If you know where the sensor is, it should give you a clue, since it's reading pressure between two things. *Probably* it's reading pressure between the compressor and the expansion valve.... so probably the blockage is the expansion valve. :) But it could also be a cooling problem, or a fill problem. I'd imagine you'd need a manifold gauge to look at the low side and make that determination.
 

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Discussion Starter #5
Alright, I have more information and this is getting interesting. My commute is a consistent 35min in the afternoon. My AC would work fine up until I was almost home. I would joke with my wife that it would work for 30 minutes and then quit. Well, I have definitive proof, but I still have questions. As I mentioned before I was sitting and watch the evap tempearture while on lunch and watching the high side pressure continue to climb. The car is parked on asphalt and today was a high heat index day, so the pressure readings sitting at idle were normal.

I drove home today monitoring the Tech2 readout all the way home. The AC pressure stabilized at 17 bar (250 psi) the entire way home. Perfectly normal. However, the Evap temperature was always reading extremely low. The reading was 5°F-6.4°F for the majority of the trip. After exactly 30 minutes, the compressor cut off, the evap temp started to rise, albeit slowly. After the evaporator melted and the temps rose to 37.4°F (3°C), the compressor would kick on, pressure would rise and the temperature would drop to 32°F (0°C). At which point the compressor would kick off. For the next 5 minutes, this cycle continued until I pulled in the garage and shut the car off. The evap drain wasn't draining at first, but after a minute or two, it started to slowly drip.

I let the car cool off for about an hour. I went down to hook up the gauges to check operation. Everything from the gauge aspect looks okay, though the low pressure side was maybe a little low, nothing was pointing to a problem. High side was steady at 250psi, low side settled in around 36psi.

I came in and opened up WIS and poked around trying to find any information about a 30 minute shutdown and of course, I could find nothing. The anti-freeze sensor has shutoff at 37.4°F (3°C) and then when temp rises to 41.0°F (5°C) it will command the compressor back on. This could be part of my problem, but it doesn't explain the ability for the system to go all the way down to 5°F and hold steady for a consistent 30 minutes before using the readings on the anti-freeze sensor.

Here is where I need some help from fellow members with a Tech2.
  • What is your evap temp reading at cold start?
  • What is your ambient temp reading at cold start?
  • With the system running, what is the normal operating temperature of the evaporator?

Is the evap temp sensor built into the evaporator? I can't find part listings for it. I'm thinking this is what is failed, but I'd like a bit more proof before I have to pull the dash apart.
 

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Discussion Starter #7
Diagnostics
Year
Model
Body
Read Values
When the list pops up, at the bottom there is a button for group listing. Pick there. Should see an option for AC
 

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Discussion Starter #9
Ah, it's in the DICE. I was trying to recall the menu order from memory.
 

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Note that at some point Saab replaced the actual evaporator temp sensor with a dummy that gives a fixed value like 4ºC. Check WIS or maybe EPC for when the change happened, I think it was late in 2002 or early in 2003 model years.


ETA: that's for the 9-5, doh. I imagine OG9-3 kept its premium (actually senses something) sensor.
 

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Discussion Starter #12
Are there 2 sensors? One built into the evap and a separate anti-frost sensor on the pipe going into the evap?
 

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There is a pressure sensor on the condenser, and a freeze sensor on the evaporator. Technically, there is also a temp sensor built into the compressor itself.
 

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The Viggen has been off for two days, but it's 100F out. Ambient temp sensor 95F. Coolant temp and evap temp are both 84F. Evap pressure is 7.8bar (113psi).

I can check tomorrow what it looks like after running for a bit.
 

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Our Civic used to stop the compressor for no apparent reason after a broadly similar length of time, then restart of its own accord (see what I did there?). I removed the shim from behind the clutch pulley and its been fine since. I suppose the gap increases as the clutch surface corrodes/wears.

Doug
 

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Discussion Starter #16
Your evap temp being the same as the coolant temp points me in a direction. When I checked mine. The evap temp was well below ambient by a long shot. I'm thinking the anti-frost is providing false numbers plus refrigerant is a touch low.

I'm going to start simple and make sure pressures are correct. I still find it suspect that DICE allows the system to keep running even though the frost sensor is showing 5°F.
 

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Ended up taking the '02 SE to work today... two weeks ago the system was totally evacuated and refilled with close to the right amount of R134a... I say "close to" because I have to fill by pressure and not weight, but the system is 770g (IIRC) and I put two 340g cans plus 60g in. The gauge set indicated things were in spec - and it kept me cool at 105F yesterday. :)

At startup coolant/ambient/evap all matched at about 70F. Within a minute or so of idling coolant was up to 120F and I turned on the AC with ACC at 68F and headed out. Coolant reached 200F quickly. Ambient stayed at 70F. Evap dived down to 40F.

During my 20 minute drive, evap stayed between 36F and 41F. System pressure moved between 8 and 11 bar. The values seemed independent of road speed, ACC did what ACC does.
 

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Discussion Starter #18
Came home this evening and decided to tear the dash apart to get to the frost sensor. Nothing out of the ordinary, just some leaves in the bottom, but nothing major. Pulled the sensor off and decided I would go pull the same part from my parts car. Low and behold, I get the same temp readings. Resistance on both sensors is the same. Swapping them and watching Tech2 gets the same reading.

The weird part is that its reading about 20 degrees below ambient. The only thing I can think of now is that my DICE is bad. Luckily I have a spare and a Tech2. I guess I'm dash diving this weekend.
 

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Discussion Starter #19
Poking through WIS. I found the schematic to the DICE. I'll do the hokey pokey this weekend and report back. I'm guessing the 20K Ohm resistor went kaput as the system still reads a value albeit out of normal range.
 

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What is component 628? A relay of some type? Or is that the actual DICE? I would personally suspect a bad connection or a wire break before a DICE that has failed in an oddly specific way.
 
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