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Ford five hundred a/c problems

Please help, I have a 2007 ford five hundred with 60,000 miles, out of warranty. I am having a/c problems. As long as the engine is revving at about 2000 rpm or the car is being driven the a/c cools fine. At idle for any length of time the a/c starts to warm up and gets progressively warmer the longer you sit. To the point it seems it doesnt cool anymore. It warms instantly so I dont think something is froze up, and when I drive it instantly cools down. I have recently had the expansion valve replaced and the system charged, this did not help. The shop were I took it to is aware it did not work, I just have to wait a day or two for the weather to warm back up again and have them take another look at it. They seem just as puzzeled as I am. Any ideas?
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Comments

  • edited April 2009
    You can be blunt or you can bring them some basic AC system diagnosis textbooks.
  • edited April 2009
    If the compressor is working correctly the problem may be the "blend door" in the HVAC system. The blend door controls interior temperature by sending incoming air through either the heater core or the AC evaporator (or both) depending on the desired temperature.

    If the blend door is vacuum controlled it could do exactly what you describe, since vacuum is high at idle and drops off as you open the throttle. At idle the blend door may start moving and direct airflow more and more towards the heater core. When you open the throttle the blend door moves back toward the AC evaporator.

    A vacuum leak would explain this, assuming the system is vacuum operated.

    Why was the expansion valve replaced?
  • edited April 2009
    Blend air door is electric in this car.
  • edited April 2009
    Well, there goes that theory.
  • edited April 2009
    mcparadise thanks for your response, I failed to mention that it seems the air temp on the right side of the car feels slightly warmer than the left side vents when this happens. The expansion valve was replaced, and I will state what was typed on my invoice, "performed a/c perfomance test, ambiant temp @80 degrees. Duct temp @70degrees. Hooked up gauges and found low side pressure was 60psi and high side pressure at 120psi. Expansion valve stuck open. Need to replace expansion valve, evacuate and recharge system." This was done, unfortunately we had a cold front come through as this was being performed and the outside ambiant temp dropped into the upper 40's and the tech was unable to check if this worked. Yesterday it was back into the mid-80's and could tell that it didnt. I am dropping the car back off tonight to have it looked at tommorow, tommorow in D/FW it is supposed to be 65 degrees so we will see.
  • edited April 2009
    I have been researching and I guess Fords are known for blend door failures, even the electronic ones. Two questions, Does anyone know were the blend door is located on my vehicle? It seems that most accessories (blower motor and various swithes) are faily easy to reach behind glove compartment and in passenger compartment? Would the compressor be bad if it works at anything above idle?
  • edited April 2009
    Can you always get hot air out when you set the control to hot? Does it then always return to cooler air when you set it to cold? If so, it is probably not the blend air door. If you have auto climate control, then there is a diagnostic test that you can run from the control head to verify the blend air door operation.
    My theory is that the compressor is not pumping enough, and that is why the mechanic was fooled into replacing the expansion valve. The faster the engine speed, the more the compressor will pump. Another thing to check is the engine cooling fan. It should be at full speed at idle with the AC on.
  • edited April 2009
    How are the pressures looking now?
  • edited April 2009
    Yes, I can always get hot air when I set it to hot and it does always get cooler when I go colder. I do have auto climate control, is the diagnostic test something I can do myself or just the dealer? I dont know what my pressures are at this time, (no gauges). I did find a TSB for 2005-2006 five hundreds #19107, mine is an 2007, for noise in the passenger compartment-air inlet door inoperative (recirculation). Could this possibly explain my problem? Are TSB's handled at Ford's expense? or are they just guidelines for the tech to work on. If I would still have to pay, I would try to put it on myself. I called the dealership and the door actuator is only $33.00, I would try to put it on myself if I knew were it is, anyone know?
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