A/C fan stops blowing on long trips

[Fallingapart]

My 05 Expedition has long had an annoying problem with the a/c. Upon start up, the a/c works fine and the fan blows on high. The unit is always VERY cold but on long trips, the a/c fan gradually stops blowing. If I put my fingers into the vent, the vent and ductwork feel very cold but there will be little to no air moving. If I turn the a/c off for 3-5 minutes or switch it to heater for a minute or so, then the fan will begin blowing at full speed again. On long trips, I have learned to run the a/c for about 5-10 minutes and then turn it off for a minute or so and then repeat. The air coming out is always very cold and the turning it on/off method will work to keep the car very comfortable - but it can be annoying to have to keep switching it on and off. And if I forget or if anyone else drives my car and they don't know about the a/c trick, then the car ends up hot. This has been going on for about 8-9 years. I have always assumed it is a vacuum hose collapsing and closing a door somewhere in the unit. I would appreciate your wisdom. Thank you!

 

[Bedrck47]

Do you have automatic or manual controls

 

[Bedrck47]

Depending on which system you have this is what the service manual shows,

• The blower motor does not operate correctly — manual climate control

• Circuitry short.
• A/C blower motor resistor.
• A/C blower motor switch

• The blower motor does not operate correctly — DATC

• A/C blower motor speed control.
• A/C blower motor.
• DATC module.

from your description of the problem I am guessing that you have the automatic system If that is the case then

AUTO

When AUTO is selected:

• The temperature control setting(s) is/are manually set to the desired setting(s).
• The air inlet door vacuum control motor is automatically controlled by the DATC module, based on the temperature setting(s).
• The mode door vacuum control motors are automatically controlled by the DATC module based on the temperature setting(s).
• The A/C compressor is automatically controlled by the DATC module based on the temperature settings. The A/C compressor will not operate if the outside temperature is below approximately 2°C (35°F).
• The A/C request button or the RECIRC request button, if pressed, will transfer the system to manual operation.
• The blower motor is on. The blower motor speed is automatically controlled by the DATC module based on the temperature settings, but can be manually overridden.

 

[Fallingapart]

Thank you, Bedrck47. I have manual controls. The a/c and blower always will work fine for a while. The a/c is always is very cold and then over time on a trip (usually about 20 to 30 minutes into the trip) the blower slows down and stops blowing. This happens on hot days and the compressor is still working fine since I can feel into the vents and they are very cold. The fan just slows down progressively until it is not blowing. If I switch the a/c on and off at about 10 minute intervals, the fan will continue to blow on high - even on 11 to 12 hour long trips. If it stops blowing and I turn it off for a few minutes or switch it to heater for about a minute or so, then the fan will again blow on high.

 

[Gapafudus]

Hey Fallingapart, I'm having the exact same problem. I have done a lone of research on this and couldn't find the fix, but I'm assuming I found what causes it to act up. Some people that have the same problem as us, say that the system freezes up on this long trips. When the a/c is on max, ice builds up slowly tail it blocks it completely. That's why when u turn off the a/c for a few minutes or turn the heater on, the heat from the engine melts the ice and then the a/c starts working properly again. It usually happens in summer time, where is very humid, I leave in San Antonio, very humid here, and I make a lot of trips to corpus christy, to the beach, where is also humid. Even tho it's only a 2 hr drive, it will happened in the first he on the road. And if I stop at a gas station, so my kids can use the bathroom, after I get back in the road the a/c works fine. Like I said I couldn't find the fix, but if u find anything, please let me know.

 

[stamp11127]

As a test, don't run the AC on max, let it pull in outside air so that the evaporator core is being hit with warmer air. If the fan continues to operate then the evaporator core was freezing up.
If it turns out the core was freezing, it may indicate the system is low on refrigerant. When it is low the evaporator core temperature drops below freezing. Add in condensate from humid air and you end up with an ice block.

 

[Gapafudus]

Stamp is there anyway not letting your evaporator core freezing up?

 

[stamp11127]

Maintain the correct refrigerant level, but only those that have the equipment can do that. When the system has the correct refrigerant level the evaporator temp is around 35-37 degrees. If overfilled the evaporator and condenser temperatures increase. Underfilled and the temps decrease, in his case the evaporator may be less than 32 degrees.
A good set of gauges will tell him what is going on, if anything.

Most people leave the system on max and at the coldest setting. As heat is being removed from the cabin the air going over the evaporator is also getting colder, sometimes to the point of being too cold. Once the temperature is comfortable you could add a little heat to the mix to keep the cabin temp in the mid to upper 60's.
Another thing to consider is the amount of heat that enters the cabin from direct sunlight and the level of insulation from the outside temp. More expensive vehicles tend to have better insulation properties and will cool quicker the base model Yugo.

The more expensive electronic systems also monitor the evaporator temperature and will cycle the compressor on/off as needed to keep it just above freezing.

Those that have manual controls may need to "defrost" occasionally.

 

[Gapafudus]

I noticed that my clutch doesn't cycle on and off, just stayes on the whole time the a/c is on. Once I turn the

 

[Fallingapart]

Thank you, Gapafudus and Stamp11127. Mine will quit blowing if on Max or on regular a/c. I'll get the refrigerant levels checked and see if that helps. Thank you!