QuestionQUESTION: My question is in reference to the AC in my 1998 Grand Caravan with dual zone cooling. First of all the car does not cool down like it used to. Running the inside fans on high both front and back and re-cirl set and the current outdoor temp during this test was about 78 deg. F. I had the windows closed and a thermometer in the center vent. This temp would not go much below 65 deg.
With the engine running and AC off I had a (134a) manifold set connected and was reading low side (LS) of 88psi and high side (HS)of 90psi. This was corresponding to 26 deg C on the gauge that is equiv. to 78.8 deg.F. I then turned on the AC and when I do this I get a loud growling sound from the compressor that eventually goes away. When it’s doing this it also seems to load down the engine (and take away power) that is more than I have ever noticed before. Watching the gauges I see HS go up a little and the LS down smoothly. When it settles down at the point of LS=20psi and HS=125psi the growling sound goes away and it sounds like a conventional compressor. The only thing is it is not cooling properly.
Looking at those pressures it looks like I am low on Freon and possibly why it is not cooling correctly. But the sound and strain on the engine makes you think it has too much Freon in the system. After the engine has been running with the AC for a while I did a “feel test” of the two tubes at each expansion valves. The one in the rear under the van, behind the rear passenger tire, the HS (smaller tube) was warm to touch and the LS (larger tube) was cool to touch, but not cold. The front expansion valve on firewall never felt this way. Both felt warm/hot to the touch. The same is true for the connections at the compressor. LS was more ambient/warm and the HS extremely hot.
One other fact I noticed was that when the AC was turned on, the cooling fans did not come on the condenser immediately. The condenser got fairly hot first then the fans came on and it kept it cool from that point on. Also when this happened the rear expansion valve displayed the same results in that the HS tube was extremely hot and LS was warm until that fan came on and cooled down the condenser. The time of running the AC before the fans come on may only be about 30sec to a minute in length.
Now that I have all the details listed I trying to determine where the problem is in the system. I think I may have a front expansion valve problem but not sure if there may be a compressor problem too. The cooling problems are even worse when it is hotter out then when I did these tests.
Thanks for any insite! JCM
ANSWER: Hi Jim,
At about 79 F the low pressure side acceptable pressure is about 135-175 psi so clearly you are low on R-134 at your current reading of 88. I am somewhat surprised that the pressure sensor is not preventing the ac clutch from activating but maybe it has to experience a still lower pressure to do that. I would be inclined to add refrigerant until you have it at the proper level on the low pressure side and then see what happens. Until you do that it is guess work to attribute the meaning of the various sounds that you are observing and other behaviors that you have been so kind to share with me. It may be that some compressor lubricant oil also needs to be added to the system along with the R-134, so consider including that in the recharge process. Please let me know how this progresses.
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Thanks,
Roland
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QUESTION: To add to my original statements above I have already added freon and because of the apparent strain and noise, I removed some of the Freon to see if there would be less strain on the engine. My real concern is that front expansion valve and whether that could be causing this. Also is that normal to have that high heat at the condenser for that period of time before the cooling fans kick on. Also is there any way to check on the compressor without removing it or breaking the freon lines. I have the same question for that expansion valve and means for checking it.
AnswerHi John,
I have a hard copy of the '98 manual which runs about 40 pages about the front system and which I can select pages from to photo copy and postal mail to you. There is an 8 step test of the expansion valve covered on 2 pages which involve the use of liquid CO2. The compressor test mainly is qualitative and mention noise issues only.
I also have the '04 manual on a CD from which I can copy pages and attach to an email. I can to the pages about testing the expansion valve and the compressor but to do that I need to know your email address. To give me that you must send me another question which you have clicked on the make PRIVATE button and in the text tell me you email address.
Let me know which you would like to have and give me the necessary in to reach you with it.
Sorry to have called you 'Jim' last time, I saw your initials 'JCM' and then didn't check carefully when responding so mentally changed the C to an i.
Roland
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