I have a 38 foot Class A gas coach. We have been struggling with the dash AC. Within the year we have replaced the dryer and the compressor. Our mechanic tells us that about 62 degrees is as cold as it will get. Is he correct? If not, what temperature can I expect to read from a thermometer placed in the center vent on the dash on a day where the outside temperature is 85-90 degrees and sunny. Thank you for your help.