A/C evaporator Temperature?? - JeepForum.com
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post #1 of 9 Old 07-09-2021, 02:46 PM Thread Starter
22george
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A/C evaporator Temperature??

2011 grand cherokee. A/C running Low side 38 psi high side 198 psi. Temp out the center vent is 68 degreesF. Put snappy solus scanner on it. Compressor is running evaporator temp is 68 degrees?? What causes this. Blend door gears were changed last year.

Thanks for the help.

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post #2 of 9 Old 07-09-2021, 04:55 PM
Jd41wk2
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2011 grand cherokee. A/C running Low side 38 psi high side 198 psi. Temp out the center vent is 68 degreesF. Put snappy solus scanner on it. Compressor is running evaporator temp is 68 degrees?? What causes this. Blend door gears were changed last year.



Thanks for the help.
Is your evaporator temperature 68 degrees or is the air leaving the supply vent 68 degrees? 2 totally different things. If it's 68 at the evap it sounds like you have moisture in the system or a low charge. Recover it. Pull a vacuum and charge it with 134a by weight. The sticker should be on the plastic piece by the radiator. I believe it's 1.09lbs in those? Not sure off the top of my head.

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post #3 of 9 Old 07-09-2021, 05:28 PM
ColdCase
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Whats the ambient temperature?. The shop manual says low side pressure should be between 20 and 30 psi in 80 degree ambient. High side between 200 and 300. Lower ambient temp, lower pressure. The evaporator should be near freezing regardless of blend door position. When operating correctly, the vent under full cold and high speed blower should be 48 F or so.

The evaporator temperature sensor is mounted close to the coldest part of the evaporator. Its primary purpose is freeze up control. It should be indicating near freezing.

So it sounds like your evaporator is not getting as cold as it should. The compressor is running, so it is probably is not the controller.

There is a cool down test if your scanner supports it. Otherwise you may be low on refrigerant, have excessive refrigerant oil in the system, refrigerant flow through evaporator may be restricted, the compressor is weak, or as jd41wk2 mentions, some other contaminant in the system.
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post #4 of 9 Old 07-09-2021, 05:38 PM
Jd41wk2
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Whats the ambient temperature?. The shop manual says low side pressure should be between 20 and 30 psi in 80 degree ambient. High side between 200 and 300. Lower ambient temp, lower pressure. The evaporator should be near freezing regardless of blend door position. When operating correctly, the vent under full cold and high speed blower should be 48 F or so.

The evaporator temperature sensor is mounted close to the coldest part of the evaporator. Its primary purpose is freeze up control. It should be indicating near freezing.

So it sounds like your evaporator is not getting as cold as it should. The compressor is running, so it is probably is not the controller.

There is a cool down test if your scanner supports it. Otherwise you may be low on refrigerant, have excessive refrigerant oil in the system, refrigerant flow through evaporator may be restricted, the compressor is weak, or as jd41wk2 mentions, some other contaminant in the system.
If the compressor was weak, the pressure differential would be much smaller. Your suction would be high and your discharge would be low. The interesting thing about these Jeeps that differ them from almost any and every other A/C system I've worked on is that they lack an accumulator. So whereas in other cars that accumulator would catch any liquid that might get passed the evaporator from low airflow moving across it, this has the suction line right up to the evaporator outlet and right into the compressor. Now Coldcase i have a question for you. Do you know what type of metering device is on the GC? is it a TXV or a capillary tube setup? Reason I ask is because if it is a cap tube and he somehow has a high charge, he should see some possible floodback to the compressor. The suction line would be sweating or iced up if it's been running for a while. Just some tell tale signs of high charge.

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post #5 of 9 Old 07-09-2021, 06:04 PM
ColdCase
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Yeah the service manual points to a malfunctioning compressor as the last possibility, which I was guessing that if the high side pressure was low because the compressor was weak it wouldn't be able to cool. But your right, there wouldn't be that much difference in pressure. Other things are more likely, and as you say the first step probably should be evacuate and recharge.

Off hand dunno, looks like a A/C receiver/dryer catches vapor that escapes from the condenser, then there is an expansion valve of the TXV design before the evaporator that, I guess, meters just enough refrigerant so all is suppose to be gas by the time it leaves the evaporator.... but I dunno off hand. It uses the evaporator temperature sensor to regulate the evaporator temperature by cycling the compressor clutch.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #6 of 9 Old 07-09-2021, 06:53 PM
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Yeah the service manual points to a malfunctioning compressor as the last possibility, which I was guessing that if the high side pressure was low because the compressor was weak it wouldn't be able to cool. But your right, there wouldn't be that much difference in pressure. Other things are more likely, and as you say the first step probably should be evacuate and recharge.

Off hand dunno, looks like a A/C receiver/dryer catches vapor that escapes from the condenser, then there is an expansion valve of the TXV design before the evaporator that, I guess, meters just enough refrigerant so all is suppose to be gas by the time it leaves the evaporator.... but I dunno off hand. It uses the evaporator temperature sensor to regulate the evaporator temperature by cycling the compressor clutch.
Oh ok great thanks! I took a quick look at mine when I pulled a vacuum and charged mine a couple summers ago and I know for sure I didn't see an accumulator off the evap but I didn't see or really look for a receiver either. Prob just didn't look hard enough lol. So thanks for clearing that up! I appreciate it.

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post #7 of 9 Old 07-09-2021, 07:02 PM
ColdCase
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The receiver is attached to the side of the condenser, one soldered together unit.
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #8 of 9 Old 07-10-2021, 09:25 AM
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I overcharged mine a few weeks ago.

Got the discharge temp down to 50 degrees. Stick a thermometer in the vent by your right hand.

Wondering what the best discharge temp is also. Would think around 40 degrees is best?
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post #9 of 9 Old 07-10-2021, 11:39 AM
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To be precise, you need to know what the temperature and relative humidity is. The temperature must be combined with the relative humidity to calculate the apparent ambient temperature ("feels like" temperature), when the temperatures are above 70 F. Use the feels like temperature for your location. This information can be obtained from multiple sources, such as the internet or local weather reports.

Insert a thermometer in the driver side center panel air outlet and operate the A/C system until the thermometer temperature stabilizes. Engine should be running 1000 rpm, doors and windows closed, transmission in park. A/C-heater controls are set to Recirculation mode (max-A/C), full cool, panel mode, high blower and with A/C compressor engaged. If the A/C compressor does not engage, you will need to diagnose that first.

Feels like 80 F and below ambient, outlet temperature should be no more that 48. 90F no more than 54, 100F no more than 59. Dunno the recommended ideal.
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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