Ok , not trying to be a smart ass here but I have a comment about the #4 and #5 , if I may.
If the airflow across the evaporator becomes compromised for what ever reason ( iced up, dirty filter, fan motor quit, fan blade came off and what ever else you can think of ) it won’t cause any of your pressures to be elevated . It will actually do just the opposite . Your eveporator pressure will decrease and with the lack of any load on the compressor your condensing temp/ pressure will also decrease as long as everything else is still working. In a nut shell a lack of air flow across the evaporator will never cause excessive condensing temp/ pressure.
now regarding your #5
At your metering device wether it be a cap tube, an expansion valve, or an orifice , when you become restricted at that location your refrigerant flow has now either stopped or nearly stopped . Now your compressor has nothing to compress. In this scenario your evaporator pressure will reduce to nearly nothing and if your completely shut off at your metering device you will even see your suction pressure go into a vacuum . ( that’s those red numbers on your Gauges below zero .)
Dosent make sense?? Ok try this at home. Start up your air compressor , let it start to fill and then slap your hand over the air intake. It wil keep running but what ever the air pressure in the tank is at that time will be all you get. It works the same in a refrigeration system . Stop the refrigerant flow and everything comes to a stand still. Stopping the refrigerant flow at the metering device will not raise your condensing pressure but there is one thing not mentioned yet that will.
He said the tractor has never been messed with so this is NOT relivent to his scenario but FYI , one easy way to get excessive condensing temp/ pressure is with the introduction of air in your system . Air is a non condensable and therefore even the smallest amount of it will result in high condensing temperatures.
How can air get in you might ask???
The most common way is when people keep adding Freon and adding Freon and adding Freon without fixing the leak. These machines don’t consume the refrigerant if there is never a leak or your system has never been opened up for service then it will never need Freon and I mean NEVER!!!!!
When a system looses enough refrigerant to allow the compressor to run below atmospheric ( or zero on your gauges) Then air is introduced through the leak because the compressor is running in a vacuum .
OK now everyone’s gonna say well it should never run in a vacuum because the low pressure switch should prevent that .
And they’re right as long as that switch works . Another way Air can be introduced into the system is through your gauges if they are not purged properly. There can also be air in your system if you have had it apart for service and did not use a vacuum pump before recharging. These are all common things that any service tech should know before working on your system.
Regardless keep in mind that a noncondensible in the system will cause the pressures he described.
Also know that a Vacuum pump serves another purpose. Not only does it removed noncondensible‘s from your system but any moisture inside has now been allowed to boil off and be removed by evaporation.
A properly evacuated , leak free system will be void of all moisture and air , both of which are considered to be a non condensable .
