When
diagnosing the auto A/C system, the difference between taking pressure gauge
readings and doing a complete and proper performance test is that the performance
test takes several different factors into consideration; not just the pressure
gauge readings.
First
and foremost, understand that in the example we’re talking about here,
depending on the temperature of the day and the relative humidity, duct outlet
temperatures of 55°F (or 13°C) may actually be normal! That’s
because when you understand the fundamentals of auto A/C systems and how
humidity really effects cooling performance, you would understand that high
humidity alone can add up to 5 times the heat load to an A/C system. That’s
right. Up to 5 times the effective heat load on an A/C system! So what that
really means is that if those duct outlet temperatures occurred on a really
hot day with extremely high humidity, you could add refrigerant all day long,
but the system isn’t going to cool any better because it’s experiencing
an extremely high heat load.
Above
that, you should understand that a ‘poor cooling complaint’ like
the one we’ve outlined here could be a result of several other problems
that have absolutely nothing to do with the amount of refrigerant in the
system.
Consider
that for this ‘poor cooling’ condition, some of the other problems
could be a result of:
1)
Restrictions in the A/C System: Restrictions in auto A/C system typically
occur at expansion valves (or orifice tubes on applications using orifice
tubes instead of TX Valves) or liquid line driers. Besides those two components,
there are really no other areas that A/C systems develop restrictions. That
is, assuming there has not been a catastrophic compressor failures, but
that’s another problem. Restrictions form in A/C systems because of
contamination and moisture. The excess moisture contamination causes the
refrigerant and moisture to react (chemically) and form harmful acids that
corrode the A/C system components. When that happens, the corrosion travels
through the system and starts to plug the smallest passages. Typically, they
would filters in the receiver drier or at the TX Valve inlet or orifice tube
inlet. When those restrictions occur, the refrigerant can not properly circulate
and that will lead to poor cooling performance from the A/C system.
2)
Poor condenser cooling: The condenser’s sole function in the A/C
system is to remove the heat that the refrigerant has absorbed in the evaporator.
To do that, the condenser must have proper air flow and all fans working
properly. In so many cases, electric cooling fans (or the switches that control
the cooling fan operations) are not functioning properly and the condenser
can not cool the refrigerant. When that happens, the A/C system will loose
cooling performance immediately.
3)
Air flow obstructions: Much like poor cooling of the condenser, when
the air flow across the condenser is obstructed, the condenser is unable
to cool the refrigerant. This has the same ultimate effect as if the fans
were not working. It’s important to maintain full and proper air flow
over the condenser assuring that all fan shrouds are in place and cooling
fans are operational.
4)
Overheating engine: Low coolant levels and poor radiators that are clogged
or missing cooling fins will cause additional heat load on the engine. When
radiators overheat, it is very common for the excess heat to be transferred
to the A/C condenser. When that happens, the condenser becomes overloaded
and can not properly cool the refrigerant. That, once again, leads to poor
cooling performance of the A/C system.
5)
A/C Compressor Clutch problems: Excessive wear and increased air gap
on compressor clutches can cause erratic operation. A compressor clutch that
can not engage all of the time will cause poor cooling performance.
6)
Air control or Air Distribution: Controls on today’s vehicles are
becoming more complicated every year, however they still encompass the same
basic functions. The controls direct air flow inside the vehicle so that
air can be directed upwards, to the defrost; downwards to the floor vents;
or out the dash vents. The A/C controls are also responsible for the
‘blend’ door. That’s the door that adjusts the temperature
of air entering the vehicle. In some cases, a bad or malfunctioning blend
door (or actuators or vacuum controls that operate the blend door) will cause
a higher mix of heated air to enter the vehicle. That heated air, mixed with
the cool air from the evaporator will reduce the cooling performance of the
A/C system.
In
short, it is obvious to see that low refrigerant is not the only cause of
poor cooling complaints. The A/C service technician must take into all the
different factors including the temperature and relative humidity of the
day plus complete a proper performance test of the entire A/C system and
all supporting systems on the vehicle. |
This
was probably one of the best books on recharging air conditioning that I
have seen...
