Here are some of the steps that need to be taken when diagnosing problems with air-conditioning systems:
When The Compressor Won't Operate
Check the wiring and make sure the proper voltage is getting to the compressor coil using a multimeter, (not sure how to use a multimeter, view this online multimeter tutorial). Without the proper voltage the coil will not have enough power to fully engage the clutch causing it to slip and burn out. This may also create heat and ruin the front seal on the pump. If there's no power at the compressor then the machines wiring harness will need to be inspected for any damage or breaks. Also the check the connections for corrosion or bad contacts, if these are found to be rusted then you'll need to clean them or in worse cases get them repaired.
All components such as the blower motor switch, thermostatic switch or pressure switch will need to be tested for proper operation. The first operation is to check the blower motor switch. The blower motor switch should pass on voltage in all three positions, low, medium and high, to the thermostatic switch. The thermostatic switch should pass on current when the switch is turned to a colder setting than what the capillary tube is sensing from the evaporator. The current will then pass through the high and low pressure switches as long as the pressure is not above the high pressure switch settings or below the low pressure switch settings. When everything is working together the current will make its way to the compressor and engage the clutch.
If the compressor still won't engage the next step will be to check the fuse or the pressure switches. Some systems have inline fuses that are wired between the machine harness and the compressor coil. This fuse will need to be checked to see if it is blown, if it is then it will need to be replaced with a suitable replacement fuse.
Check the compressor to see if it's working, if the current is getting all the way to the compressor coil and it won't engage you will need to check the compressor for proper grounding. The coil will need to be tested for proper operation. If the coil is okay, check the clutch for any damage or for a gap that is too large between the plates preventing the coil from engaging. With all of these components working correctly the compressor should now engage.
What happens when the inline fuse is blown
If the fuse was blown it needs to be replaced, once replaced and the compressor is running the cause of the fuse blowing needs to be found. AC systems that have a fuse are designed to blow when the compressor starts to pull a vacuum from being low on refrigerant to protect itself from locking up. When the compressor is engaged watch the low pressure it will start off at its equalized pressure but as the compressor starts to pump it will pull a vacuum when the system is low on refrigerant.
On some models with a fuse setup it will have a low pressure sensor on the back of the compressor that will ground out the fuse causing it to blow and shut off the power to the compressor. Once the fuse is blown the system will not run again until the fuse is replaced. Systems that do not have a fuse will have a low pressure switch. This switch will sense low pressure and cut off the power to the compressor. After the compressor shuts off the pressures will equalize, the low pressure switch will sense that the pressure is up and will re-engage the compressor until it senses a vacuum again. It will then shut the compressor off again, this will continue to cycle until the proper amount of refrigerant is added to fill the system. If the system is low on refrigerant check the system components for leaks. There are two ways to do so using a Freon detector which actually draws in air and tries to detect the scent of refrigerant gas informing you where the leak might be. Another way to find the leak is by using the die detection method where dye is injected into the system along with the refrigerant. It is best to do this at the time of original installation of components this will help the dye to show up at the site of the leak when it occurs. The dye will only glow under a black light, this method works very effectively and is a fast way to find a leak. If there's a faulty line MalpasOnline carries a wide variety of replacement lines that can be found referencing the original equipment manufacturers part numbers (OEM). Having the actual type of connection of the line is also very helpful since the system on your tractor could have been altered at some point in time.
Depending on the refrigerant used, one way to find out if the system is full is to look into the site glass and look for bubbles, you can use this way to fill the system by watching the site glass while filling keep adding refrigerant until the bubbles have disappeared. Perhaps the best way is to evacuate down the system with a reclaimer to remove all Freon and start from the beginning adding the proper amount per manufacturer specifications. If at any time you are unsure on filling the system then you should seek profession help.
Low Pressure Diagnostics
After checking for proper refrigerant levels if the system is full but the gauges are showing a vacuum on the low side a plugged expansion valve could also be a possible problem. If this is the case the system needs to be evacuated and the expansion valve must be replaced with a new one. When doing this the system will be opened and the receiver dryer will also need to be replaced. MalpasOnline has them categorised by machine model however a visual check of the size, style and connector type can also be identified in our online range. If you determine that your expansion valve is defective we carry several styles. The block style looks like this one below, all block style expansion valves appear to be the same but are made with different port and thread sizes. The o-ring and flare style will look similar to the image below but are available in different fitting sizes. This style expansion valve is built with a variety of capillary tube styles
(Expansion valve styles, Flared & O-ring)
High Pressure Diagnostics
Let's take a look at the high pressure gauge to determine if there's a problem. High side pressure in normal conditions will be around 150 psi depending on the ambient temperature this can range from 100 to 250 psi. The higher the ambient temperature the higher the pressure gauge will read. If the gauge is reading higher than normal pressures the first thing to check is the condenser. When the temperature is excessively high it means the condenser is not being cooled down and will need to be checked out. The condenser must be cleaned and unrestricted from dirt to work properly. When the fan does not cool down the condenser the temperature will steadily increase until the pressure switch shuts the compressor off. On systems with a high pressure switch the switch will cut off power to the compressor until the pressure comes down, after the pressure comes down it will reengage the compressor. On systems that don't have a high pressure switch they will have a superheat switch that will blow when it reaches 430 psi, this is located on the backside of the compressor. Once this switch is blown it will need to be replaced. The condenser must have proper airflow to cool the refrigerant to bring the high-pressure gas to a liquid state. If it's not cooled down properly it will cause the whole system to heat up and may cause the compressor to fail prematurely. If you find your condenser or evaporator to be defective or damaged MalpasOnline sells new replacements, they are categorized by model application in the air conditioning section.
Older Agricultural Vehicles Without Air-conditioning
If your tractor is not fitted with an air conditioning unit then did you know that one be can retro-fit as described in Farmers Weekly online. They say that "fitting an air-conditioning unit to an older tractor, handler or combine that didn’t come with it in the first place can be complicated and costly. However a new quick-fit system from French manufacturer Hygloo could make the process simpler and cheaper. Typical cost of the whole system is £1,950. Not cheap, but it could make life much more pleasant for any driver in an older tractor having to do long hours in hot weather."
Looking for other Air Conditioning Parts?
NEW: Have you seen our new website dedicated to cab blower motor assemblies? Visit www.malpasairflow.co.uk