Pressure Gauges Readings with the Hood Up or Down?
When you're diagnosing auto A/C system, there really is a
you're performance testing an auto A/C system, should you take pressure gauge
readings and duct outlet temperatures with the hood up or down? When you
think about it for a minute, it may appear pretty difficult (not to mention
tricky) to get pressure gauge readings when the hood is down, but there is
a good reason why you may want to.
that the air inlet for the A/C system is right at the base of the windshield.
Typically, the air inlet will be covered with a screen to prevent debris
and other foreign material from falling in. You should also notice that between
the air inlet and the engine compartment, there is a long rubber strip that
runs the entire length of the firewall. That's a really important piece of
rubber when it comes to keeping you cool!
a 'hood seal'?
long strip of rubber on top of the firewall is the hood seal. With the hood
open, you should be able to see where that rubber contacts the hood from
one side to the other. When the hood on the vehicle is closed, that rubber
strip or hood seal prevents hot under hood air from being drawn into the
air inlet of your car's air conditioning system. When the hood is up, instead
of drawing outside ambient air temperature of 80° F or 90° F into
the air inlet, you're pulling hot under hood air that could be 200°
F or more!
it really mean?
the most part, when diagnosing and testing auto A/C systems, you should be
all right doing that with the hood up. You should be able to take pressure
gauge readings and perform your tests without problem. However, understand
that in cases where there is poor air circulation (typically inside service
shops) and the vehicle is being operated for extended periods of time, there
will be a continued increase in A/C pressures and duct outlet temperatures.
order to check or verify the A/C system, lower the hood. Use caution not
to get the manifold gauge hoses caught or damaged, but with the hood lowered,
you will start to see an improvement in the gauge readings.
sever applications or problem jobs, a good tech tip is to set up the gauges
in a way that you can actually close the hood. That will provide you the
most accurate pressure gauge readings and duct outlet temperatures for the
A/C system. There is a difference and the pros will use this trick to assure
themselves that the A/C is really working properly.