When I'm sitting or at city speed my ac works fine, but when I get to hwy speed it quits and fan doesn't kick on. However, if it's cloudy it works fine on the hwy (honestly). I checked the pressure and it was low so I charged it. Now it blows really cold until I hit the hwy, then its back to hot air. Talk to intl they dont know or won't venture a guess, and I'm not ready to drop a grand+ on it yet. I have a replacement high pressure switch to install, but haven't had an opportunity to put it in yet, anyone have an idea of the problem.
Heating / Cooling No ac at highway speed
- Thread starter Wdelsey72
- Start date
The most common cause of the AC not cooling at high speeds is low freon. The second most common cause is like low pressure on the high pressure side. You should have the system pressure checked at various RPMs. If the high pressure side is too low, it'll simply disengage the compressor clutch, and thus not cool until the RPMs on the engine fall back down.
Is the coolant flow to the heater core shut off? There should be taps or valves to do it. Those Maxxforce engines reject a TON of heat at highway speeds and loads, making sure those valves are closed is essential.
You also may have some air in the system....charging it up is ok but not if the end result still contains air.
If the htr core valves are shut and it is still an issue, find an A/C shop and have them do a vacuum pulldown and recharge on the system...easiest and cheapest place to start.
You also may have some air in the system....charging it up is ok but not if the end result still contains air.
If the htr core valves are shut and it is still an issue, find an A/C shop and have them do a vacuum pulldown and recharge on the system...easiest and cheapest place to start.