Air conditioning recharge question

Discussion in '2005+ Mustang GT 4.6L Tech' started by CJ-, Sep 6, 2017.

  1. CJ-

    CJ- forum member

    I’ll start by mentioning, I know that if I have to recharge the ac system with Freon, I know I have a leak, I know I should have a ac tech diagnose it, I know it’ll eventually leak out and I also know that stopleak could damage components of my ac system which could cost me more money to repair than if I had taken my car to an ac tech to have it diagnosed properly.

    Ok with that out of the way... the past 3 weeks, my ac hasn’t been as cold... cold but not as cold as it used to be.

    Also the compressor would click on and off every 1-2 seconds everyonce in a while depending on conditions (ex:stop and go traffic in 90+ degree weather or when accelerating aggressively and sometimes click off for minutes at a time before it decides to click back on.)

    I decided on buying a recharge kit (big can of r134 with hose and pressure gauge). I got the engine to operating temperature and turned the AC to full blast. Compressor is spinning and staying engaged with no issues previously mentioned.

    Hooked up the recharge kit to the low pressure line and with ambient temps at 75 degrees at the time, low pressure line shows 25-26 psi.

    I use this chart I found here:
    70f 25-45 psig
    80f 30-50 psig
    90f 35-55 psig

    So I’m shooting for 37 psi, I start filling her up and immediately the lines get ice cold and colder air is coming out the vents and I proceed to get a mechanical hard-on.

    Once half the can is sucked into the lines, the gauge reads 30 psi, I’m shooting for 7 more psi so I continue to charge with 4 second bursts every 15 seconds... now the can is nearly empty and I’ve only achieved 1 more psi so I’m at 31 psi and I empty the rest of the can into the system and still... 31 psi.

    I drive for an hour and AC is ice cold during idle but isn’t as cold during acceleration, ac clutch isn’t disengaging like before so that’s good and the vents got so cold that condensation formed around the vent bezels.

    Cut to this morning, ac still cold but drove for an hour and Ac loses its cool slightly acouple times for a minute during idle and during acceleration...

    My question, Does that mean I could need another Can of r134?
  2. 86GT351

    86GT351 forum member

    System is low on Freon most likely. The coolness is because as you drive you have cooler air coming across the A/C Condenser. This helps allow the freon to flow more efficiently. If it is low on charge there is not enough for the system to work properly,
  3. CJ-

    CJ- forum member

    Copy that, thanks for having patience with my long post
  4. 86GT351

    86GT351 forum member

    LOL. I work in a dealership Service Department. I deal with it all day!
  5. 07 Boss

    07 Boss forum member

    Get a set of gauges and hook them up to the high and low ports. That can tell you a lot if you have a component that may be going out or not functioning properly. Just because your static pressure is good doesn't mean that the AC is working as it should. You know you have a leak somewhere and that leak may be the result of a failing component.

    Balthazor72 likes this.
  6. 46addict

    46addict 13726548

    Once you verify pressure, scan for codes and look for any misfire faults. I say this because you mentioned the AC gets warmer during aggressive acceleration. I know the PCM shuts down the AC compressor when the engine misfires.
  7. Wes06

    Wes06 forum member

    I'm pretty sure the engine cuts ac during hard runs regardless of misfires.
    Conserves hp from running the compressor and gives it all to the tires
    Humanoid likes this.
  8. 07gts197

    07gts197 forum member

    Op I had a similar problem a few years back. I started noticing it not working really well during the day but pretty good at night. It slowly got to the point where I knew I wasnt crazy and it actually was getting worse. It ended up being my evaporator core. That was a huge headache but the shop I went to quoted me 1200 bucks, but I did it with about 200 and I took my time.

    If theres a shop nearby that does free diagnosis then I would do that sooner than later so you know what youre dealing with. It could be as simple as an old o ring or a leaking evaporator core and you have to remove the entire dash.
  9. mfergel

    mfergel forum member

    Double check the AC Compressor clutch/pulley. I was having a similar experience a few weeks ago. It would cut off and on weird while I was trying to charge the A/C. A few days later I started hearing noises. Turns out, the rubber bushings at the front of that A/C clutch had either rotted away or fallen out at some point. That in turn must have messed up the bearings in the pulley. I bought a kit at Autozone that includes a new coil, pulley and clutch/hub. Been running like a champ since and the clicking in and out when it should is working fantastic. May not be the issue but doesn't hurt to double check. I'd do a visual inspection and then loosen the belt at the tensioner and hand spin the AC pulley to make sure the bearings are OK.
  10. groundpounder

    groundpounder forum member

    While not directly related to the mustang, I had a similar issue with my F350. Had a mobile tech come out. We checked everything. Hi/low pressure switch voltage, freon pressure, dash wiring, etc. Spent 4 hours trying to figure out intermittent AC operation. Swapped relays, bypassed hi/low switches and just couldn't figure it out. He had access to a master Ford tech who was guiding us deeper into the trouble shooting checklist. Finally at one point he pushed on the relay in such a way that he felt it click and the clutch engaged. Turns out the contacts were dirty! Cleaned them with a little Emory cloth and presto, full working AC. My suggestion is start with the small)easy stuff. Wiggle the wires/connectors/relays and see if that gets you anywhere.
  11. boomer9999

    boomer9999 Junior Member

    If the AC compressor clutch is engaging and disengaging in short bursts of like 1 second, the r134a is probably low.

    Idk about my 07 mustang, but I just fixed my 97 f150 ac. The AC on the F150 has a UV dye in it to find any leaks. Just use a UV light and look around all the connections and compressor. My problem was a compressor shaft seal that was blown. I did learn a few things.

    There is something called an orifice tube in the pressure line from the compressor. If this tube is plugged up (it has a built in strainer) then that can impede flow of the freon and oil. My 20 year old tube was almost perfectly clean. No teflon or metal shavings.

    I fit a new condenser, lines, compressor and orifice tube. Then I flushed the evaporator with AC flush. Next, pulled a vacuum for a few hours and waited an hour to make sure there were no leaks. Injected proper amount (12oz) of freon and 7oz. of AC oil with a few teaspoons of UV dye.

    I've never done AC work before, but with the help of utube videos and some work I've got ice cold AC again. I did have to buy a set of guages (like the ones 07 boss) used and a vacuum pump. Low side pressure is like 37 to 40 and high side is 200 to 300 psi at 80F.

    I think with the full guage set and uv light you can diagnose better.
  12. Balthazor72

    Balthazor72 Junior Member

    Question: after changing clutch (tranny), my compressor isn't operating at all in ac. I do have the check engine light on and the wrench symbol on my dash. I'm assuming the PCM is not starting my compressor until I do my drive cycle to activate all my sensors, correct? 08 GT
  13. Wes06

    Wes06 forum member

    Double check you didn't disconnect the clutch on the compressor or something. My car has no problem turning the an on after battery is disconnected
  14. ox white

    ox white forum member

    Absolutely not. A/C will work regardless of whether or not a drive cycle (DTC P1000 set) has been completed.
  15. Balthazor72

    Balthazor72 Junior Member

    Weird! I guess it's coincidental that my compressor stopped working after I put things all together as it was working fine before. I checked and all is connected as it should be.
  16. 07 Boss

    07 Boss forum member

    What is the CEL for?

    Double check the wiring harness that runs by the tranny. I’ve heard of a few cases where that got pinched moving or removing the tranny and it’s caused issues like this. It’s a stretch but might be worth checking out.
  17. s8v4o

    s8v4o forum member

    This is absolutely correct.

    Also the condensation very well might be from when the compressor kicks off (ie wide open throttle). When that happens you will be pumping air with a high moisture content through a system that's cold. When that happens you will certainly develop condensation.

    Next time it's low use a proper gauge set to put in a can of freon WITH UV dye in it. Then get you a light from Amazon like this to find the leak. It very simple. You don't have to get the yellow sun glasses but boy does it help cut down on that UV glare and help you pinpoint the leak better. If you have any questions feel free to ask.
  18. Juice

    Juice forum member

    This actually is telling me you have TOO MUCH r134a in the system. A/C is usually not as cold at idle as higher cruising rpms (1500 &up) While the low pressure is a good indicator of charge level, I don't swear by it. I'm old school, and when I charge an AC system, I grab the discharge line from the evaporator while adding r134a. As soon as I feel that hose get cold, I stop adding r134a and call it done.

    The quick compressor cycling is due to the low pressure switch in the system. When pressure drops to a certain level (and low charge makes this worse), the compressor shuts off to prevent the evap from icing up and block airflow. The compressor should cycle unless it is really hot out there and the system is working 100%.

    Note: It has been so hot around here, I had to use recirc/max a/c because the air didn't feel all that cold with ac on fresh air. So a lot of this cycling depends on the heat load on the car. Full sun vs night time etc. You get the idea.
    Balthazor72 likes this.
  19. jhunt47

    jhunt47 forum member

    Something to check as well. I was having a leak as well that was loosing Freon in about 2-3 weeks time. What I eventually found was the high side Schrader valve itself was leaking. It was a bit harder to find as while the gauges was hooked up no vacuum was lost. After the charge all was good installed the caps and went on with it. Then the a/c performance would die down. I only found it when I was charging through the low side only and heard hissing. Traced it to the high side removed the cap and that’s when I found it. Replacement was 15 dollars which included both sides plus 31oz of Freon.
    Last edited: Aug 10, 2018
  20. Balthazor72

    Balthazor72 Junior Member

    Nowadays systems come precharged with dye already in the I found when I guaged up to the system for the first time.