I have a 2006 Mustang GT. The air flow through the vents has been erratic. Sometimes the air will blow through the vents and sometimes it doesn't. The temperature control works fine as it blows hot air or cold air depending on the setting. Once the fan kicks in, I will get the speed that it is set on the fan switch. If the fan doesn't kick in, I can still feel cold air barely blowing through the vent. I have replaced the resister under the glove box and I still have the same problem. Any suggestions. It is hot here in California and I need my A/C!!!. Thanks