AC questions: works better when moving

[bhuff30]

I got the AC blowing cold again for the first time in about 2 years this week. So great to have AC again, however I can tell the air is quite noticeably warmer when the car is at a stop. It is warmer yet when I am at a stop for a long period. While moving, it feels great. I'm guessing this is due to an inadequate fan?

These cars have a 2 speed fan, correct? About 2 years ago, my the fan motor burnt up and I bought the cheapest fan available (motor only) from rockauto to get going again. Is it possible the fan I purchased is only a one speed fan, allowing for some cooling while stopped, but not enough for the AC on a hot day? Is there any way to check or verify two speed function?

I know the fan runs, but I think it just doesn't push enough air. When charging the AC, I used the assistance of a garden hose on the condenser to get the high side pressures down, otherwise, the high side pressure was excessively high without even getting a full charge. Ohh, and when it isn't an insane 100* with 104 heat index, the AC can keep up pretty well while stopped. It always feels fine at speed though.

 

[Noobz347]

You need to move more air through your radiator and more importantly, the air conditioner heat exchanger.

I have to assume that the fan you're talking about is your engine cooling fan and not the blower fan for your HVAC. While it may move enough air for your radiator to keep up with the motor, there's just not the same amount of surface area for the A/C heat exchanger.


The fix... move more air.

 

[bhuff30]

Well, sounds like my theory of insufficient fan is correct, but now I am looking for the issue and solution.

These cars have 2 speed fans, correct? Is it possible or common that parts places would sell single speed motors? The rest of the system is pretty much standard. The condenser is clean and not clogged up, and I've never had engine cooling issues (despite my attempts through aggressive driving ).

 

[wmburns]

The GT Mustang has a two speed fan. The Low speed fan normally runs when the AC is on. The high speed fan runs when ever the AC high pressure switch is tripped or the motor temperature is above the high speed fan set point.

Normally above 45 MPH a fan is not needed so the PCM turns it off. Hence the reason the AC works fine when the car is moving.

I suggest starting off by testing the fan. The low speed fan wire is R/O. The High speed is O/LB. The ground is black. Run the fan directly from battery. Battery negative to black. Battery positive to R/O and the low speed fan should run. Move the probe to the O/LB wire and the high speed fan should run. There should be an obvious difference in the fan speed.

If both speed fans run, the next step is the test the CCRM.

 

[bhuff30]

Perfect, this is exactly the information I was hoping for! Soon as I get the chance to give this a try, I will report back. I fully expect the fan motor I purchased to be a single speed motor, but makes the solution obvious (and easy enough).

I suggest starting off by testing the fan. The low speed fan wire is R/O. The High speed is O/LB. The ground is black. Run the fan directly from battery. Battery negative to black. Battery positive to R/O and the low speed fan should run. Move the probe to the O/LB wire and the high speed fan should run. There should be an obvious difference in the fan speed.

If both speed fans run, the next step is the test the CCRM.