Puzzling reading on AC gages.

[Snagglefoot]

I had a leak in my AC system over the winter and lost some pressure. It was properly loaded in last fall after putting it on vacuum. There was still some pressure in it so I wanted to pressurize it again and check for leaks. ( there is dye in the system)

I’m up in Canada and use propane based refrigerant which is legal up here and it’s not considered ozone depleting, so leaking off into the atmosphere is just a cost consideration at $8 US equivalent per can.

The compressor was not running. I loaded in one can and the compressor came on and cycled between 24 and 52 psi on both sides and the vent was still blowing warm.

I then loaded a 2nd can and the compressor came on on full time and the pressure was 100 psi on both sides and the vent was blowing cold air at 49 F.

I don’t know why the pressure is the same on both sides but is still able to cool the air. Thoughts? Thanks.

 

[Wrenchturner44]

Does the car have a POA valve.....common on older cars with AC?

 

[Snagglefoot]

Does the car have a POA valve.....common on older cars with AC?

Not sure. It’s a 2008 Suburban and the front system has an orifice tube. The rear Ac has an expansion valve I believe. I did change out the orifice tube last fall.

 

[Snagglefoot]

Here is a screen shot of the video I made. Both gages are reading 100 psi. The ambient temp was 75 F and the vent temp was 49 F. The compressor was running continuously.

 

[brages]

Maybe your gauges are broken? Try it on another car..?

 

[Chris142]

Did you close both valves on the gauges?

 

[Gladtojoin88]

It holds 3 lbs 36 ounces. Most the cans are 12 ounces. Be careful on using the bigger cans because they contain too much oil and if you end up with too much oil the pressures will be wrong too!

 

[Gladtojoin88]

I mean 48 ounces . 16 ounces in a pound I believe sorry!

 

[mk378]

As @Chris142 said, that will happen if you are not using the manifold properly by closing the hand wheels to take pressure readings. With the valves open, refrigerant will pass through the center of the manifold and both gauges will read the same or nearly so.

Also since the HC refrigerant is a blend, it can fractionate as it leaks out and you end up with an improper blend in the system just by topping up.

 

[Snagglefoot]

As @Chris142 said, that will happen if you are not using the manifold properly by closing the hand wheels to take pressure readings. With the valves open, refrigerant will pass through the center of the manifold and both gauges will read the same or nearly so.

Also since the HC refrigerant is a blend, it can fractionate as it leaks out and you end up with an improper blend in the system just by topping up.

Ok thanks. So the the knobs on the manifold just give access to the yellow hose port ( and by default to the other gage) and not to isolate the gage from the AC line. I’ll give it another try tomorrow.

 

[Snagglefoot]

Here is my rookie mistake. This cross section shows that the valves in the manifold isolate the high and low pressure from the yellow hose. This diagram shows the knobs going off to the sides but the Pittsburg manifold has the knobs turned 90 degrees, coming out of the page but achieving the same result. Dooh.

 

[LazyDog]

Usually when high and low pressure are the same it means AC compressor not on. If my car sits overnight and hook up the gauges, I should read the same pressure on the low / high side call static pressure. This reading would tell me if I am low on Freon.

 

[Jetronic]

I had a leak in my AC system over the winter and lost some pressure. It was properly loaded in last fall after putting it on vacuum. There was still some pressure in it so I wanted to pressurize it again and check for leaks. ( there is dye in the system)

I’m up in Canada and use propane based refrigerant which is legal up here and it’s not considered ozone depleting, so leaking off into the atmosphere is just a cost consideration at $8 US equivalent per can.

The compressor was not running. I loaded in one can and the compressor came on and cycled between 24 and 52 psi on both sides and the vent was still blowing warm.

I then loaded a 2nd can and the compressor came on on full time and the pressure was 100 psi on both sides and the vent was blowing cold air at 49 F.

I don’t know why the pressure is the same on both sides but is still able to cool the air. Thoughts? Thanks.

are your gauges connected properly?

 

[Jetronic]

Usually when high and low pressure are the same it means AC compressor not on. If my car sits overnight and hook up the gauges, I should read the same pressure on the low / high side call static pressure. This reading would tell me if I am low on Freon.

That tells you what the temperature of the freon is, but not more unless you're extremely low on fill: to the point that the system doesn't work.

 

[Jetronic]

Here is my rookie mistake. This cross section shows that the valves in the manifold isolate the high and low pressure from the yellow hose. This diagram shows the knobs going off to the sides but the Pittsburg manifold has the knobs turned 90 degrees, coming out of the page but achieving the same result. Dooh.

View attachment 157986

Should have rad further before commenting. Glad you found it though

 

[zzyzzx]

I have had issues with the Harbor Freight quick disconnect (end pieces that connect to the vehicle) whereby it doesn't open the valve in the car, depending on the car (as if not enough travel).

 

[Snagglefoot]

With gage valves closed and the compressor cycling I’m getting 20-40 psi on the low side and 50 to 70 psi on the high side. The ambient temp was 81 and the vent temp was 66 degrees F with the AC set at 68 F. I’ll continue to check for a leak. There is dye in the system.

 

[Snagglefoot]

Here is a photo under a black light. I’ll torque down down the connection to 16 ft lbs to see it that can seal it. Notice the bright refrigerant on the low side port where I loaded refrigerant. Enjoy.

 

[Mcbeem5]

With gage valves closed and the compressor cycling I’m getting 20-40 psi on the low side and 50 to 70 psi on the high side. The ambient temp was 81 and the vent temp was 66 degrees F with the AC set at 68 F. I’ll continue to check for a leak. There is dye in the system.

 

[Snagglefoot]

View attachment 158193

Thanks. I was looking for this type of example. I think I’ll try fix all the leaks, then look at a new compressor.