Vacuumed and Charged 2 Vehicles & Have The Same Problem.

[needhelp]

Hi,
I am working on my wife's 2007 Mazda Miata: New condenser, High and Low port valves, 16oz R134a added and 1.5 oz pag oil
Also my 2005 Jeep Grand Cherokee: New Refrigerant line, new expansion valve, High and Low port valves, 24oz R134a added

Ok so I borrowed Gauge Manifold set and Vacuum pump from Orville's. The low side reads 2psi resting, high 0. When connected High and Low pressure are identical so I assume pressure is accurate when over 2psi.

I vacuumed down to 28, never hit 30, but I assumed that is the 2 psi error and it did go to 30 vacuum pressure (or however you say it)

Let vacuum for 45min with both high and low valves open. Then shut the valves and turned off pump. Connected refrigerant with engine off opened low valve and added about 15psi, then started engine and charged the called for weight.

The pressures varied, but when done low side was about 30 and high about 150 on both cars. Ambient temp about 80+ F.

I am new to a/c work, but the compressors will not shut off. From what I understand the high side pressure will climb to a threshold and then the pressure switch will trigger the compressor to shut off. Then this continues, on and off on off... Both cars the high side just sits at 150psi and compressor does not shut off unless I turn off a/c or press the a/c button on controls in vehicle.

I am not sure what I did wrong. Both cars are the same. Did I freeze up expansion valve on charge? Do I need to let the vehicles sit for a few hours?? Please help. Thanks

[JohnHere]

I can't help but wonder about your charging procedure and whether you've done it correctly. The reason I say that is because at one point you mention weight, and at another you mention pressure.

Regardless, the charge amount must be weighed-in exactly to the manufacturer's specifications.

Under most practical circumstances, one cannot charge a system by pressures. The pure refrigerant (no sealer or other additives allowed except for UV dye) must be weighed in, either by using an accurate refrigerant scale, or by means of a professional RRR (Recovery, Recycling, Recharging) machine, which typically only professional shops have due to the cost.

But even before discussing charging, the systems must be evacuated to about 29.9 inches of mercury (InHg), and then charged into the well-held vacuum. If you are located at an elevation notably above sea level, that vacuum reading will be correspondingly less.

As well, I'm curious about why you replaced the components that you did.

Also, the static pressures don't sound right. They should be approximately equal to the ambient temperature that in this instance is about 80°F.

For reference, the specifications I have for the 2007 Miata are 16 ounces net weight of R-134a refrigerant, and 4.4 fluid ounces of PAG-46 oil unless the under-hood decal says otherwise.

And for the 2005 Grand Cherokee, the specs are 24 ounces net weight of R-134a, and 4.5 fluid ounces of PAG-46.

[needhelp]

I can't help but wonder about your charging procedure and whether you've done it correctly. The reason I say that is because at one point you mention weight, and at another you mention pressure.

Regardless, the charge amount must be weighed-in exactly to the manufacturer's specifications.

Under most practical circumstances, one cannot charge a system by pressures. The pure refrigerant (no sealer or other additives allowed except for UV dye) must be weighed in, either by using an accurate refrigerant scale, or by means of a professional RRR (Recovery, Recycling, Recharging) machine, which typically only professional shops have due to the cost.

But even before discussing charging, the systems must be evacuated to about 29.9 inches of mercury (InHg), and then charged into the well-held vacuum. If you are located at an elevation notably above sea level, that vacuum reading will be correspondingly less.

As well, I'm curious about why you replaced the components that you did.

Also, the static pressures don't sound right. They should be approximately equal to the ambient temperature that in this instance is about 80°F.

For reference, the specifications I have for the 2007 Miata are 16 ounces net weight of R-134a refrigerant, and 4.4 fluid ounces of PAG-46 oil unless the under-hood decal says otherwise.

And for the 2005 Grand Cherokee, the specs are 24 ounces net weight of R-134a, and 4.5 fluid ounces of PAG-46.

Yes I weighed the refrigerant. 16oz exactly and 24oz exactly. The pressures 30 and 150 were engine on a/c on pressures. The 150 would hardly move and the compressor would stay on. If I understand right the high side should continue to go up until pressure cut off switch shuts off compressor and then this cycle begins again.

The miata had a damaged condenser so I replaced it and came with a new dryer. The jeep had a leaky valve and the low side broke when taking it out. Part was stuck in the line, so I replaced the line and high valve.

Static pressure engine off was even pressure on both sides. I charged to 20 psi first because the mazda manual said charge to 20 psi check for leaks, charge 7oz (total engine off steps), then start engine and fill the remaining refrigerant.

I am wondering if I put too much LIQUID refrigerant in at first before the engine was on. The manual didn't say gas only. So I used the 12/3 o'clock method on the cans instructions.

Could putting too much. Liquid in ruined the refrigerant mix in the system? That is the only thing I can think I maybe did wrong. Also I partially opened the manifold valve to not rush to much in at once, maybe I should have gone wide open with gas only....

[Cusser]

I'm not an AC professional, but good-working systems do not continuously build up high side pressure until the high pressure switch cuts off the voltage to the AC compressor. The high pressure reading will stabilize depending upon several factors, including ambient temperature, air flow over the condenser, engine rpm.

Typically, high side pressures with R134a at 80F ambient at 2000 rpm run from maybe 150 psi to 250 psi; you can look up values yourself, that's just off the top of my head.

Please wait for others to comment.

[Tim]

Does the pressure change when you give the vehicle increased RPM? Gauges should be closed when checking.

[needhelp]

Ok, well in my old age I guess I am loosing patience...

Once the systems warmed up and the cabin got ice cold. The compressors both cycled about 3-4 times a minute at 75- 80f

Pressures were on point to. The miata specs are lower than my jeeps for the high/low side pressure. I am sure that is due to the compressor design/make. But were both in spec.

I think on initial startup cold engine, it takes maybe 20-30 min for everything to build and warm up/ chill.

Sorry for jumping the gun but we are good to go!!! And 1 month or so before super hot days in the south. Couldn't be happier

[JohnHere]

Those of us who have a long history of working on MVAC (Mobile Vehicle Air Conditioning) systems generally do not rely on shop manuals for pressure readings. Experience plays a part. In addition, a number of parameters can and will affect pressures, only one of which is ambient temperature.

Compressor cycling will occur due to various operating conditions, as already pointed out.

Anyway, glad that you were able to solve it and that both vehicles' systems are now operating and cooling properly—just in time for the upcoming summer in the South. Seems I know about that all too well