A c Continually Cycling on and Off
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New compressor (twice), dryer (twice), pressure switch (twice), fan switch, control panel (dash), thermostats and blend door motor. Full charge of freon and it still cycles off after approx.10-15 seconds then back on after about 30 seconds. Pressure low side drops to about 30psi High side might get to 150 before it kicks off. 60 degrees ambient. It's cooling the truck but I fear it's wearing out the clutch. I've switched out relays and fuses as well as replacing the fuse holders. Can anyone point me in the right direction?
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More than one pressure switch in that system. Did you change all? Sounds like you have a air flow problem, dirty or restricted air flow across evaporator. Also dirty condenser will cause that but your high pressure side would be higher.
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What switch kicks the compressor? Low side or high side? High side usually wont kick til 300 or so. Low side is 20 ish depending.
Bypass the one switch to narrow down which one is causeing issues.rolls canardly and SAR Thank this. -
Also might try removing the condensor and cleaning the air side of it. Also clean the air sides of the CAC and radiator while things are apart.
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what kind of truck is this in it could be the thermistors there is no reason for that clutch to kick in and out i would check the setting on the freeze switch or the evaporator doesn't have good air flow and its freezin up to soon this is where i would start nothing to do with psi or fan problems, this would be start, thermistor are a suggestion if it is a prostar in that case i would also suggest expansion valve .
spsauerland and Heavyd Thank this. -
Thank you! WHAT KIND OF TRUCK?????????
Trucks are all different out there guys! They aren't the same, better know what we have here before we send this guy on a wild goose hunt. -
2007 Freightliner Columbia Condo with 14 litre Detroit. The pressure switch is binary and handles both low and high pressure cutout. Bypassing it doesn't help. Compressor still cycles constantly. Entire HVAC unit was removed to replace a blend door at the Freightliner dealer in Hattiesburg, Ms. about 3 years ago ($5,000). I wouldn't recommend using them. The bunk blower doesn't work. Replaced blower motor, thermostat and computer module in bunk but still doesn't work. I should also mention I replaced the blower motor in the cab after reading it could cause the problem I have. To clarify the thermostats I mentioned were the two thermistors that install before and after the evaporator. The fan switch I mentioned is the fan clutch activation pressure switch on the dryer.
Is there anyway to bypass the temp sensor to test for a clogged evaporator or is there a way to visually inspect it without complete removal?
Last edited: Apr 21, 2018
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No this is not normal for this truck or the other Columbias I have. It has always stayed on at least a few minutes before cycling due to thermostat.
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Doesn't the body computer have something to do with this?
I had a truck back in 2009 which we replaced every a/c part and still had issues until the regional tech came in and replaced the body computer which solved the issue. He said that the body computer takes the control setting from the havc cab controls and tells the ecm to switch on the compressor, and add a little bit more fuel to the engine at idle.
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Source: https://www.thetruckersreport.com/truckingindustryforum/threads/a-c-clutch-constantly-cycles.890902/
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