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Gauge reads dangerous high pressure level?

hekg on Mon May 11, 2009 4:58 PM User is offline

Year: 1999
Make: Chevy
Model: Tahoe
Engine Size: 5.7
Refrigerant Type: 1394a
Ambient Temp: 90
Country of Origin: United States

Hi all,

My a/c has started to take a very long time to cool lately. When I first get in the car it's taking alot longer than usual before hot air stops blowing out and replaced with cool air. I realize that the temperature outside is very hot here in Miami lately but it is definitely taking much longer than it should to cool though.

I suspect that I have a slow freon leak since I had to have some added about two years ago for the exact same problem.

I bought one of those autoparts store all purpose cans with the hose and gauge. I got rid of the can and hooked up a virgin can of 1304 freon and hooked it up to the hose and gauge. When I turn my car on and run the a/c on max, I then connect the host to the correct port but the gauge immediately reads in the red danger levels.

I really suspect that my freon levels are low but why does the gauge go to the red immediately?

Thanks for any help that you guys can offer.

Cussboy on Mon May 11, 2009 9:32 PM User is offline

Only use a real pressure gauge manifold, need to know both low and high side pressures at about 200 rpm.

iceman2555 on Tue May 12, 2009 9:26 AM User is offlineView users profile

Recently had a conversation with an associate that imports items such as this 'manifold/gauge' set. Seems that the cost of these 'tools' is much less than a buck. Boggles the mind that these darn things will register pressure at all.
A good set of gauges is essential for correct AC pressure evaluations. "Topping off", as this individual is attempting to do is not an acceptable method of AC service. The refrigerant should be recovered and recharged using the correct equipment. Using pressures to determine correct recharge rate is 'hit or miss' for the best of techs...for a DIY'er.....seems to be the 'SWAG' method.
An undercharge of 5-10% may be detrimental to compressor longevity.....system performance may be acceptable.....but the compressor may starve for lubrication.
A question concerning the length of the hose for this gauge assembly.....most of the units I have seen have a very short hose...less than a foot. If this is the case, how did one attach a 30lb can to the suction side of the system.....if not not the suction side of the compressor on this vehicle located on the manifold at the top/rear of the compressor. If this is indeed, the case...know that it is very easy to liquid slug a compressor on this vehicle.
It is quite possible that the 'red' reading associated with this post is actually the pressure reading within the refrigerant container and not the system itself.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

mk378 on Tue May 12, 2009 10:12 AM User is offline

Attempting to charge by pressure is only valid when the compressor is engaged. If you have some charge in the system but the compressor is not engaged, it is normal to see a pressure of about 100 psi (depends on temperature) on the low side.

The compressor should engage when the pressure is 50 psi or higher. If not, there is some problem other than lack of refrigerant. Cooling intermittently suggests a clutch gap problem.

The high side pressure is a more useful metric when charging by pressure. A single gauge on the low side is beyond useless, it is dangerous.

hekg on Wed May 13, 2009 6:52 PM User is offline

Thanks for the advice, I think I will just have to bite the bullet and take it to a pro this time.

JJM on Thu May 14, 2009 10:52 PM User is offline

No such thing as red and green with auto A/C work. Those silly little gauges are only good to smash on the ground.

With the right tools - like a proper set of gauges - and the willingness to learn you could be as good as some who call themselves pros.


When considering your next auto A/C purchase, please consider the site that supports you:

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