New guy here. I’ve got a 2021 579 that randomly started blowing hot air even when the ac is on. I was going to unplug the high and low pressure switches to see if that fixes it but idk where they are. The fan runs constantly and it being 94 in South Dakota/Montana with no ac sucks. Any help is appreciated.
Help. 2021 579 that randomly started blowing hot air
Discussion in 'Peterbilt Forum' started by martin_ky_86, Jun 9, 2023.
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A recharge is fairly cheap and only takes an hour or two max and will rule out a huge host of issues. I usually need to do one a year on my 17 579 to keep the AC in tip top shape and if you havent done one yet that could be the issue especially if it has a very slow hard to find leak like my unit.
Also go to the peterbilt in watertown if you can. They handle my rig for day to day issues and are good trustworthy folks if a tad pricy.martin_ky_86 Thanks this. -
Oxbow Thanks this.
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I feel bad for this person, I do, but how can you justify spending, what, $200grand on something, that 2 years later, doesn't work? It's unacceptable and if it was me, that tractor would be parked crossways in the dealers entrance with 10 flat tires. I just don't understand how we got to this point,,,
gekko1323 Thanks this. -
If it blows cold air for a while, then suddenly quits I would say its safe to assume the charge is good. What you need to do is find out if the compressor clutch is still cycling on/off or not when it starts to blow hot air.
If the compressor is not kicking on (and there's refrigerant, which sounds like there is) - most likely a wiring issue. Although too high pressure on the high side/too low on the low side will trip the switches, but the system should kick back on once the A/C pressures start to equalize and fall back within the threshold of the switches.
If the compressor is cycling and there's hot air out the vents, check the evap drain isn't plugged, the core will start to freeze up if it is and it'll start blowing warm air.
A/C manifold gauges are worth having for diagnosing A/C problems. -
I've found there's a connection between the sleeper berth controls and what blows up front. I can't explain why, but when I turned the temp control in back to the cold side, I suddenly had AC up front. It was a hot day until I stumbled across that weird bit of engineering.
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You could get one of those cans of refrigerant with a pressure gauge on it. They're sold at almost every auto parts store, maybe even truck stops or Walmart. If you do find it's low and decide to add refrigerant, use it as a temporary fix only. You need to find where it's leaking from and fix it, and if you continue to just add refrigerant it gets expensive, plus you can get moisture in the system and damage other components. If you can't get into a dealership to have it fixed, you should be able to use any auto AC repair place to at least get it diagnosed.
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201 Thanks this.
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