Help. 2021 579 that randomly started blowing hot air

Sounds more like something inside your compressor system borked. When my 579 did the same thing one of my lines had cracked. Nothing for it but to replace the line and recharge it. Usually hot air only is a sign that the R134 is low/gone. Id try a recharge first and ask them to put dye in if it doesnt already have dye. Or to check for leaks. If it pulls a vaccum and had full pressure well thats a whole host of otger issues it could be. If it was low or cant pull a vaccum then its a leak and needs fixing.

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.

 

Does it blow hot air all the time, or does the cold air come and go?

 

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,,,

 

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.

 

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.

 

Also, not one truck has an interior that is worth a ####. Cheap fixtures, things breaking, etc.

 

That's a shame, but typical of today, nothing is sacred anymore. My old Pete( in avatar) was a good old horse, and my '82 WS was better than that. This is the price we pay for modern gee-gaws, and outsourced parts, where failure rate, as in that compressor, is just figured into the cost later. It keeps those cheap compressor makers in China working. When the compressors were made by York, that could cool an office building in, in good ol' YORK, Pa., I never recall an issue aside from coolant leaks. He'll get it fixed, just in time for winter, then ,,WHAT? No heater cores? Don't laugh, happens all the time at Freightliner. I would wish them luck, but luck has nothing to do with it today, and just a sign of the times.