Quirky A/C performance

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  #1  
Old 09-09-15, 07:44 PM
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Quirky A/C performance

2002 Suburban 1500 with rear air. At idol there is no A/C and the compressor short cycles on/off within 1 second. At speed or with load on the engine, the A/C performs perfectly. When tested, the compressor seemed to be pulling to the same pressure before cutting off (50 psi) regardless of whether the engine was at idle of at speed. I replaced the low side cutoff switch with no change in performance. I should note that I tried jump the leads on the low side cutoff switch and the compressor seemed to act exactly the same.
 
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Old 09-09-15, 07:54 PM
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You're saying that you bypassed the low pressure switch and the compressor was still cycling at idle ?
 
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Old 09-09-15, 07:58 PM
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It was kind of like there was a bad connection at the harness. But it acted exactly the same as if it was going through the low pressure switch. I would have assumed that jumping the leads would cause the compressor to run continuously. It short cycled same as if hooked up.
 
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Old 09-09-15, 08:31 PM
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I've read of a reference to a trinary switch. It's in the high pressure line and it monitors the high and low ends of the high pressure system. If your vehicle has that... it will also cause the compressor to cycle.

I've found listings for a high pressure switch. No mention of a trinary switch.
Trinary is a valid type of high pressure switch but no mention of use in your Suburban.

You may want to locate the high pressure switch and bypass it to see if affects the cycling issue.

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Old 09-10-15, 04:55 AM
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That looks like the low pressure switch that I replaced. I'll be honest, I could not find the high pressure switch when I looked before. Is that a picture of the high pressure switch? I'm just baffled by the idle vs load difference in performance.
 
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Old 09-10-15, 10:59 AM
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It might be cycling on high pressure. Make sure the fan clutch is working correctly and pulling enough air over the condenser, also make sure the condenser is clean, no leaves or debris blocking it.
 
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Old 09-10-15, 06:37 PM
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From what I see the low pressure switch is at the compressor and looks different from the high pressure switch. Don't go by the color. The color is the operating pressure.

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Old 09-10-15, 06:47 PM
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Here is the switch I changed out. Again, I have no clue where the High Pressure switch is located. This was the low which was attached to the condenser (I think) right up against the firewall.

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Old 09-11-15, 02:16 AM
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the switch you changed was probably on the accumulator and should of been the low pressure cycling switch. it generally near the firewall round cylinder shaped.
the condenser is in front of the radiator the high pressure switch is probably on the compressor itself.
the fact it works good going down the road would probably look at the fan or fan clutch without pressure readings really hard to say whats going on, but before using a jumper to bypass a switch you could take a garden hose to the condenser if the compressor stays on at idle with water running over the condenser then its likely cycling cause of to high of pressure do to the fan not pulling air through the condenser.
 
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Old 09-14-16, 12:45 PM
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Going to resurrect this and say that the solution was indeed the fan clutch. Took this long as I did not fully understand how to test for a bad fan clutch. Watched a video or two recently and determined that it was worth the investment to see if it corrected the problem. So hats off to Tom and Allen for being spot on!
 
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