Check the low pressure switch which is located under the jump seat . Had problems when it started to cool down at night -- unplugged it and now no more problems . With the cab windows fogging up it is moisture left in the condenser evaporating after you shut off the ac . My suggestion is to have the cab air filter clean so the little pressurizing fan can supply fresh air to clean out the moisture and to use a combination of heat and ac to keep the temp at desired .Another thing is to take the seat off and to blow or wash out the evap core once every two years as it will get dirty because most of the air in the cab is recirculated through the cheap foam filter behind the seat .