AC Manifold Gages Issue

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crash68

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if going off a static pressure to determine leakage when the system is charged with refrigerant you need to reference the starting and subsequent ambient temperature readings and compare the two a 134a PT chart. A change from 80° up to 90° raises the pressure almost 20 psi. With the system pressure changing it's difficult to determine if there's a leak, nitrogen is temperature/pressure stable.
134a_PT.jpg
 

Sherman Bird

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Hey Sherman,

I for sure am going to replace the Schrader valve, empty the system, and fill it back to the proper level. I don't trust that Schrader valve at all. When I drove it this morning the air stayed at 60 degrees. Now 6 hours later the air cycles between 65 and 80. I think it is losing quite a bit of r134a in a very short time
If your HVAC is losing refrigerant that quickly, then you have improper system oil distribution. Oil tends to leave the compressor and flood the evaporator when there is frequent loss/refill going on. I've seen this MANY MANY times over 46 years professionally. This sets the stage for eventual compressor failure all because of ignorance and improper procedure. This is why the owner's manual and the underhood information label, telling how much and what type refrigerant and oil capacity are required is there, warns to have only "qualified personnel" perform service.

If the evaporator is oil flooded, it must be flushed, and the condenser has to be flushed as well. This requires hazardous chemicals that require PPE be used such as a respirator, goggles, and nitrile gloves for your protection.

Next, you must determine IF the compressor has the proper amount of oil in it. Most cases, you have to remove the compressor and drain it into a graduated container.

It IS a PITA, for sure, but doing it correctly the first time prevents aggravation and insures proper service life of the system.

Also, a word to the wise: ALWAYS replace the accumulator or desiccant bag or entire condenser (required in some situations), and vacuum the system for AT LEAST 45 minutes! I hope this helps!

BTW, I lost a friend to an A/C system explosion years ago... due to him failing to use personal protection gear and following proper protocol. Years later, a co worker had a can of refrigerant IN HIS HAND with the engine running and him topping off his A/C. The can unexpectedly exploded! The bottom of the can went through the steel hood of his F-150 like it was soft butter! He couldn't hear for a week afterwards! The ONLY thing that saved his eyesight was the protective eyewear he was wearing pursuant to shop policy!
 

Sherman Bird

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if going off a static pressure to determine leakage when the system is charged with refrigerant you need to reference the starting and subsequent ambient temperature readings and compare the two a 134a PT chart. A change from 80° up to 90° raises the pressure almost 20 psi. With the system pressure changing it's difficult to determine if there's a leak, nitrogen is temperature/pressure stable.
View attachment 499685
Nice chart..... I have them, too, in my shop. Those figures are VERY subjective, but good basic guidelines to about where the pressures should be.

Humidity, air flow, engine RPM at the time of test, along with time to allow the system to get stabilized. Also, is the vehicle in direct sunlight?, or inside a shaded albeit hot shop?

Over the last month, I had 2 very dark colored vehicles (ironically both Hondas) that I worked on the A/C refrigerant part of the systems. The temperature here in Houston was a scorching 104 degrees with humidity in the 70%-up range.

I performed acid tests on them both post repair: Leave them outside with the windows up tight in direct 3 PM hot sunshine for an hour.

In both cases, the inside temps exceeded 160 degrees, and upon opening the driver's door to get into them, heat waves emanated just like when you open an oven door.

The outlet temperatures according to the chart weren't exactly as shown on those charts until the vehicles were driven a while.
 

Sherman Bird

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Nice chart..... I have them, too, in my shop. Those figures are VERY subjective, but good basic guidelines to about where the pressures should be.

Humidity, air flow, engine RPM at the time of test, along with time to allow the system to get stabilized. Also, is the vehicle in direct sunlight?, or inside a shaded albeit hot shop?

Over the last month, I had 2 very dark colored vehicles (ironically both Hondas) that I worked on the A/C refrigerant part of the systems. The temperature here in Houston was a scorching 104 degrees with humidity in the 70%-up range.

I performed acid tests on them both post repair: Leave them outside with the windows up tight in direct 3 PM hot sunshine for an hour.

In both cases, the inside temps exceeded 160 degrees, and upon opening the driver's door to get into them, heat waves emanated just like when you open an oven door.

The outlet temperatures according to the chart weren't exactly as shown on those charts until the vehicles were driven a while.
Nitrogen constitutes 80% of the air we breath. It is a poor leak finder where one can't gain sight reference. I use CO2 and a CO2 leak detector AND dye AND soapy bubbles! All are necessary and each has it's best place. I never charge any system past 200 PSI when I use CO2 for leak detection. This is to prevent damaging those soft gooey aluminum components! Ahh! I'm remembering the good old days when condensers and evaporators were made of brass or copper! ;)
 

crash68

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Nice chart..... I have them, too, in my shop. Those figures are VERY subjective, but good basic guidelines to about where the pressures should be.
There's nothing subjective about that chart at all, if that's what you think then your knowledge of refrigeration is limited.
 

Sherman Bird

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There's nothing subjective about that chart at all, if that's what you think then your knowledge of refrigeration is limited.
Subject to variations in humidity, engine RPM, and how much air is drawn across the condenser. Yup! Subjective in a non static reality of automotive HVAC. Those numbers would be more precise in a non ambulatory unit such as that one in my house. Also, the home unit operates at a fixed RPM. Peace!
 
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Sean J Blackburn

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I used the static pressure chart posted up earlier and it was over filled. I bled the system until it was down to 116 at 96 degrees.

Vent Temps at idle went down to 50.5 and while driving drop to 43.3. I think it's probably good now.

Still not sure why my low side never showed above 40psi but everything appears to be working for now.

I appreciate everyone's help with this!
 

Sherman Bird

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I used the static pressure chart posted up earlier and it was over filled. I bled the system until it was down to 116 at 96 degrees.

Vent Temps at idle went down to 50.5 and while driving drop to 43.3. I think it's probably good now.

Still not sure why my low side never showed above 40psi but everything appears to be working for now.

I appreciate everyone's help with this!
For future reference..... You can read the temperature of the metal part of the suction hose both at the firewall end and the other end of it close to the compressor while the engine is running and the A/C is turned on. The temperature should be within 10 degrees of each other in a properly working system. IR temp sensors do not work on this. You should use a contact sensor, like the ones on nicer multi function meters have. Mine is a lifesaver because that way of determining proper refrigerant level is pretty accurate BUT NOT a substitute for gauges.
 

JosephPukala

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If your HVAC is losing refrigerant that quickly, then you have improper system oil distribution. Oil tends to leave the compressor and flood the evaporator when there is frequent loss/refill going on. I've seen this MANY MANY times over 46 years professionally. This sets the stage for eventual compressor failure all because of ignorance and improper procedure. This is why the owner's manual and the underhood information label, telling how much and what type refrigerant and oil capacity are required is there, warns to have only "qualified personnel" perform service.

If the evaporator is oil flooded, it must be flushed, and the condenser has to be flushed as well. This requires hazardous chemicals that require PPE be used such as a respirator, goggles, and nitrile gloves for your protection.

Next, you must determine IF the compressor has the proper amount of oil in it. Most cases, you have to remove the compressor and drain it into a graduated container.

It IS a PITA, for sure, but doing it correctly the first time prevents aggravation and insures proper service life of the system.

Also, a word to the wise: ALWAYS replace the accumulator or desiccant bag or entire condenser (required in some situations), and vacuum the system for AT LEAST 45 minutes! I hope this helps!

BTW, I lost a friend to an A/C system explosion years ago... due to him failing to use personal protection gear and following proper protocol. Years later, a co worker had a can of refrigerant IN HIS HAND with the engine running and him topping off his A/C. The can unexpectedly exploded! The bottom of the can went through the steel hood of his F-150 like it was soft butter! He couldn't hear for a week afterwards! The ONLY thing that saved his eyesight was the protective eyewear he was wearing pursuant to shop policy!
It is frustrating when considering all the regulations, protocols, and environmental and energy codes that I have to deal with to hold a professional class A unlimited license and then see threads like this and people can just buy r134a at Walmart and just “bleed” it off. The max penalty if I release refrigerant into the air is up to 10 years prison and 250k in fines.
 

JEFF MANN

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Purging air is a very simple process and must be done every time a vehicle is connected to a manifold set, just very briefly back off the hose connection at the gauge set, same with the yellow charge line. air can be harmful to the system as well as messing with pressures. During my years as an Ambulance Mechanic I would purge with nitrogen, vacuum & recharge.
 
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Sean J Blackburn

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Just to conclude this thread I took the truck into a mechanic. They vacuumed it and recharged and said that the charge was a half pound low. The pressure was OK, but charge of r134a was low. I do believe air must have been introduced into the system to give a correct pressure reading with a low charge of refrigerant. All is good now.
 

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