Cooling fan Not Working Running and Properly Charged

[Mark Kelly]

Hey guys and gals bought a used 2005 mustang AC not cooling as well as it should. Hooked my AC gauges up to it low and high levels were where the should be pressure wise with it NOT running. Started engines watched gauges High side climbed higher that it should, noticed the fan wasn’t running on low like it IS supposed to, the high/low fan resistor was bad, common problem with these year models. Replaced the whole fan assembly, resistor is anywhere from $70 to $150 depending on where you get it from. So if you AC isn’t cooling like it should make sure you have it on Max, Inside blower motor (fan) is on high and Recirculation Switch is on if you have one. Now start engine and check to make sure you compressor is engaged and you engine cooling fan is on Low it should run when you AC is in the above state,, if all the above states are met place a temp probe in the air vent. You can get one for a few dollars off line or at a parts parts/tool store. If your AC is working properly you should see the temp drop to about 45 to 38 degrees at 2000 RPM. At 75 to 85 degrees out side temp the high side pressure should read from 150 to 180 psi with the engine cooling fan on low. If you fan isn’t on low but coming on and off on high and your pressure is building on the high side more then 225 psi you have a problem. This high pressure will cause early compressor failure over time. I tested my Low side fan using jumper wires and found the resistor has burned out thus I replaced the whole fan assembly and tested it before installation,,, but guess what fan would still not come on low and stay on like it was supposed to. After further testing I found where when the old resistor burned out it had melted one of the connections on the under side of the fuse box under the hood that housed the low fan relay. Thus I had to pull the upper part of the fuse box and repair ( this is tedious) and must be done right or just replaced the fuse box. Once done I retested using the fore told steps fan running on low constantly with AC on max, low side pressure stayed at 32 and high side never got above 175 psi at 78 degrees out side temp, inside temp pulled down to 50 degrees at a 800 rpms brought engine up to 2000 rpms and inside temp dropped to 38 degrees in about 5min high pressure side came up to 180 psi which is OK. My pony car has 160,000 miles on it and is the original AC unit. So if your having this problem follow the steps above to see if this is also your problem... PS I went through many threads to try and find what I found through much diagnostic testing...