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1997 STS
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9 Posts
Discussion Starter #1
My 1997 STS air conditioning only engages the compressor when I slow to stop, and then works only momentarily, (cool air for about 10 sec.). It has a full charge and there are no codes. I can bypass the relay and engage the clutch, no problem. :banghead:

Any ideas?

Thanks.
 

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Super Moderator
2010 DTS
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87,559 Posts
Something else is going on. Speed has nothing to do with compressor engagement. What are your high and low side pressures?
 

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1997 STS
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9 Posts
Discussion Starter #3
I know it seems odd but it engages randomly and only for a few seconds, usually after driving a few miles and then slowing to stop. After that it kicks in a little more often until it sits a while again.

I'll throw the gauges on tomorrow and double check. I do remember the low would easily go to 100 and the high would continue to creep past 350 if I let the clutch stay engaged for more than a few seconds at a time while recharging. I put the recommended 2lbs of refrigerant in.

Tends to want to go high on both sides. I do remember I had a heck of a time getting it to take refrigerant as the clutch would not engage by itself. I checked to make sure there were no codes to clear, that wasn't the problem.

thanks.
 

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2010 DTS
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That was such a long thread I don't remember, but I don't think you had hight pressures, did you Nitro? Cruizer, yours are high. Sounds like a blockage somewhere. Might need to pull the orifice tube and have a look at it. It doesn't sound like it is running long enough to ice up.
 

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1997 STS
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9 Posts
Discussion Starter #6
Hmmmm...worth checking. I had the high temp go out last year, but got a definite code that took me right to it.

Thanks, I was actually following that thread yesterday but didn't get the ending...
 

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1997 STS
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Discussion Starter #7
That was such a long thread I don't remember, but I don't think you had hight pressures, did you Nitro? Cruizer, yours are high. Sounds like a blockage somewhere. Might need to pull the orifice tube and have a look at it. It doesn't sound like it is running long enough to ice up.
Well, now that makes sense especially since I recently had to remove the receiver/dryer to replace the power steering pump. May have gotten some crap in there. I thought I kept everything clean and closed up well enough, but you never know.
 

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2010 DTS
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Did you pull a vacuum before charging it? If not, then icing is a distinct possibility. I doubt you got anything in it. Usually when the compressor starts to go, debris will clog the orifice tube and cause problems. I think high pressures on the high side will be one. I'm not sure how or if it affects the low side.
 

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1997 STS
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Discussion Starter #9
Did you pull a vacuum before charging it? If not, then icing is a distinct possibility. I doubt you got anything in it. Usually when the compressor starts to go, debris will clog the orifice tube and cause problems. I think high pressures on the high side will be one. I'm not sure how or if it affects the low side.
Yes, I pulled a vacuum for about 35 minutes.
 

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2005 White Diamond STS N* 1SF RWD ACC/HUD
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I had a similar issue with the A/C on my car recently. The orifice tube was clogged with debris. Works great now.
 

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1997 STS
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Discussion Starter #11 (Edited)
Something else is going on. Speed has nothing to do with compressor engagement. What are your high and low side pressures?
OK...I put the gauges back on this morning. Compressor off: Low side - 75, High side - about the same. Clutch engaged manually: Low side - 30, high side - 175. Nice cold air when engaged. Those don't seem like bad pressures.

I'm thinking a sensor problem at this point. I've checked the compressor relay - good. Low pressure switch - good. Ambient temp is right on. Inside temp should be OK since it reacts normally to manually adjusting inside temp and fan goes on and off accordingly.

I'm wondering if Nitro might be right about that high temp switch. You would think I would get a code though since it never engages.
:hmm:
 

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1997 SLS
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550 Posts
That was Shawn's (Nitroshark) experience - it did not throw a code, but your symptoms sound a lot like his. You'll have to evac to change it out though.
 

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Cadillac Seville STS 2003 47000 miles
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128 Posts
What was the outside temp when you got your pressure readings? The reason I ask is the low pressure cut out will shut the comp off when the low side starts getting below 20 psi. If you are at 30psi at idle, as soon as you speed the engine up, the compressor will pull the low side down pretty fast. Place the gauges back on the system and have someone increase the rpms to 1500-2000 rpms and see how fast the low side goes down. If the outside temp is in the mids 80's -low 90's , I charge a system to around the low 40's psi on the low side. That will prevent it from cycling so much when driving down the road.
 

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97 SLS & 06 STS-4 Cadillac
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Those numbers do seem a little low when looking at the FSM ( This may tell us something later to look at). You said you put the full 2 lbs in and pulled vacuum so if there is no leaks you should be good.

As for a easy test, Go get/make up a 3.8K resistor. Pull the plug off the A/C low temperature sensor (it’s the small 2 wire thermiser I had to replace) and jumper the plug.

Start the car and see if the compressor now runs nonstop. Do not jumper anything else.

If the compressor runs non stop for at least 3-4 min’s I bet your sensor is bad like mine was.

Shawn
 

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1997 STS
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Discussion Starter #15
Still pulling my hair out on this one. I checked the low and high side temp sensors using a resistor...no problem there. I even pulled them out and checked them visually and ohmed them against a new one. I went ahead and replaced the orfice tube and recharged the system with 2lbs refrigerant.

Don't know why but it cycles more often now than it did, however it still kicks out prematurely, about 5 seconds on and 30 seconds off. Just starts to cool the air nicely then kicks out and blows warm air until another 30 seconds or so.

Today the outside air temps were warm here, around 90 degrees. My low side was dropping to about 50 before kicking out, and goes to 120 before engaging. The high went to around 250 - 260.

I'm wondering if this be a faulty high side cut out switch? I believe it's located down at the compressor.
 

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Super Moderator
2010 DTS
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87,559 Posts
Something is wrong. Those low side pressures are WAY too high. Low side pressure should be around 27.
 
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