2003 Ram 4.7L Why would the air work perfectly until stopping at a light and hear a little sound then starts blowing very hot air instead? Even when put in neutral and revved up doesn't help, until the truck is in motion again it will not get cold again. I've also noticed that every time the truck is turned off you can hear a hissing for maybe 6 seconds. I've drained all the refrigerant and pulled a vacuum and refilled it with top notch 134a and it's made no change except gets a little colder. The refrigerant never gets low either, what's causing this?

  • What pressures are you getting on the high side and low side? Do you know how much refrigerant you've added and is it what Dodge recommends? – Zaid Aug 14 '16 at 11:44
  • The refrigerant I used was what the local dodge dealership recommended and I seconded that using my fluid specs catalog in Advance and O'Reillys computer systems, I don't exactly remember my exact pressure numbers but with my guage I was at about 75% up into the recommended safe zone levels. It works wonderfully, as long as you don't make a complete stop. – TRIGGA Aug 14 '16 at 12:20
  • 1
    It sounds like the fans aren't kicking on with the AC. I'm assuming the Ram has electric fans. If you're not getting the air flow through the condenser when it's sitting still, you won't get much cooling from the AC. The hissing sound you're hearing is normal ... just the refrigerant pressures equalizing in the AC system. – Pᴀᴜʟsᴛᴇʀ2 Aug 14 '16 at 12:37
  • How is it that it works perfectly as soon as you start moving again though? Its almost like a disengagement kinda sound it makes as soon as the truck stops rolling and as soon as that sound is heard the air switches to heat it feels like. It can't be the blend door though could it cause how would it know to switch as soon as you stop? I ruled that out already, but a very similar sound to that though. Like on an older car when pushing the lever from cold to hot how you'd hear that door switch over, almost identical sound from deep in the dash. – TRIGGA Aug 14 '16 at 13:22
  • The pressure in the ac system probably goes too high when you stop moving with no fans running. The high pressure trip will disengage the compressor until the pressure drops when you start moving again and so the cooling will start. – HandyHowie Aug 14 '16 at 13:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.