Weak Compressors, or bad orifice tube?

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99dubj
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Weak Compressors, or bad orifice tube?

Postby 99dubj » Sat Aug 01, 2020 7:16 pm

Hello all, fairly new to ac repair but not vehicle repairs. I could really use some help.

I have a 1999 jeep grand cherokee 4.7l that is mostly for offroading/weekend car. The old compressor let go while driving a few weeks ago. I actually heard it go and the vent temps became hot immediately (I always have a temp probe in them). I wanted to save some cash and try to do this myself (famous last words).

Fast forward to last week and I replaced the compressor, condenser, accumulator and the liquid line w/ orifice tube. I flushed the evaporator and the remaining high side line. New schrader valve on that line as well. Added oil to the accumulator line, about an ounce extra since I didn't get a proper reading from the old compressor but the "new" compressor came with oil. Vacuumed the system for 2 hrs and left it overnight. No leaks. Starting filling the next morning and everything started going well until the high side got to about 80-90 and completely slowed down. At that point the low side began to climb. After slowly adding 2 12oz cans my pressures were L:47 H:125 Vent 62 degrees. Later on that day in the heat they were L:57 H:175 vent in the 70's. At that time probably 90 degrees out.

With those readings I figured weak compressor so I bought a "new" one from my local parts store. Vacuumed for 1 hour and let it sit for an hour holding vacuum. No leaks. Same exact results with the newer compressor! Last night was around 84 degrees, humidity 78%. L:56 H:165 vent temp about 64.

Am I just killing compressors, or is it possible I have an issue with the liquid line with the orifice tube? is it possible I received a defective orifice tube/wrong size? Would that cause pressures like mine?
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bohica2xo
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Re: Weak Compressors, or bad orifice tube?

Postby bohica2xo » Sun Aug 02, 2020 6:10 am

The system capacity for that GW is 26 ounces of refrigerant, and 7.5 ounces of PAG 100 oil.

You are undercharged on refrigerant, and at an unknown oil charge level.

When you replace a compressor, drain the NEW one. It is unlikely that there was a full 7.5 ounces in the replacement compressor.

Testing should be done with the doors open, cabin fan on highest speed. Engine rpm 1500 to 2000. Idle testing does not give a true picture of the system.

It is possible to kill a compressor with an inadequate oil charge, and a prolonged charging process. NEVER use a jumper to run the compressor while charging. If it is short cycling, let it do so, and get some more refrigerant in it as quick as you can.

Get us some pressures from a proper load test, and we can evaluate from there. 1500+ rpm, high pressure / low pressure / vent temp / ambient. Run at 1500+ for 3 minutes & take the data while still above 1500 rpm
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Cusser
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Re: Weak Compressors, or bad orifice tube?

Postby Cusser » Sun Aug 02, 2020 10:14 am

I seem to read that you bought a new compressor (among other stuff) but then bought another new compressor because you didn't trust the first one?

Were both compressors brand new, and the same part number/brand???
99dubj
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Re: Weak Compressors, or bad orifice tube?

Postby 99dubj » Sun Aug 02, 2020 3:55 pm

bohica2xo wrote:The system capacity for that GW is 26 ounces of refrigerant, and 7.5 ounces of PAG 100 oil.

You are undercharged on refrigerant, and at an unknown oil charge level.

When you replace a compressor, drain the NEW one. It is unlikely that there was a full 7.5 ounces in the replacement compressor.

Testing should be done with the doors open, cabin fan on highest speed. Engine rpm 1500 to 2000. Idle testing does not give a true picture of the system.

It is possible to kill a compressor with an inadequate oil charge, and a prolonged charging process. NEVER use a jumper to run the compressor while charging. If it is short cycling, let it do so, and get some more refrigerant in it as quick as you can.

Get us some pressures from a proper load test, and we can evaluate from there. 1500+ rpm, high pressure / low pressure / vent temp / ambient. Run at 1500+ for 3 minutes & take the data while still above 1500 rpm


For 99, my service manual and hood decal state 24 ounces refrigerant. It also calls for ND-8 oil which I read to be a PAG 46 oil. The service manual states 4.40 ounces of oil + whatever else is in the compressor. I added 5 ounces of PAG-46 to the accumulator line when I installed the first compressor. The second compressor came with a label on the manifold block off plate that stated it had 2 ounces of oil. I added 1 ounce to the current compressor. I should have drained it first so that was my mistake.

Compressor was never jumped to run, and it actually never cycled because the low side never dropped below 30.

I added 2 more ounces of refrigerant to get these readings. Temp was 88 degrees and humidity 70%. Doors open, fan high and 1500 rpm's readings are L:57 H:225. Vent temp was 72-74 degrees.

Cusser wrote:I seem to read that you bought a new compressor (among other stuff) but then bought another new compressor because you didn't trust the first one?

Were both compressors brand new, and the same part number/brand???


Yes, based on what I paid and where I bought the first compressor I assumed it was a weak rebuild. They were not the same brand/part number. Second one was listed as new.
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JohnHere
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Re: Weak Compressors, or bad orifice tube?

Postby JohnHere » Sun Aug 02, 2020 5:52 pm

Elevated pressure on the low side along with minimal or no cooling could be due to an incorrect orifice tube, as you queried. Are you sure that you have the correct OT installed (part number and color), and is it facing the right way? The screen should face upstream, or away from the evaporator.
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bohica2xo
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Re: Weak Compressors, or bad orifice tube?

Postby bohica2xo » Sun Aug 02, 2020 5:57 pm

Book vs underhood sticker - sticker wins. Jeep tends to change systems mid year.

Your high side is in line with a proper charge with that ambient.

A restricted OT could certainly cause problems, but this could be re-heating as well. Is the accumulator cold?
99dubj
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Re: Weak Compressors, or bad orifice tube?

Postby 99dubj » Sun Aug 02, 2020 7:26 pm

Thank you so much for the reply guys! I appreciate your help troubleshooting.

Jeep does change alot midway! In 01 they went with the expansion valve in this model and also increased refrigerant to 27 ounces.

So in this vehicle the orifice tube is crimped in the hard line so no real way for me to check/replace it without replacing that liquid line. The replacement part was for my vehicle model, I didn't really check on colors but it did say it included a green orifice tube with a certain part number. I will check what that model and size is.

I cut the old line open and the tube looks blue. I will look up those 2 colors for the size difference.

The accumulator and lines seem cold, lots of condensate on them and also a good amount coming from the drain line.

Last year while my old compressor was working, I was troubleshooting some blend door problems and I took some readings at idle. Most likely same weather, I am in central Florida. L:46 H:230 at idle! So I definitely have something mismatched in here.
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bohica2xo
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Re: Weak Compressors, or bad orifice tube?

Postby bohica2xo » Sun Aug 02, 2020 9:46 pm

A cold accumulator with 74f discharge air indicates some blend air entry.
Dougflas
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Re: Weak Compressors, or bad orifice tube?

Postby Dougflas » Mon Aug 03, 2020 1:24 am

bohica2xo wrote:A cold accumulator with 74f discharge air indicates some blend air entry.


I agree 100%. Block off or by-pass the heater core.
Al9
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Re: Weak Compressors, or bad orifice tube?

Postby Al9 » Mon Aug 03, 2020 1:43 am

Or turn the AC on while the engine coolant is still cold. Get a better vent temperature that way and here's your problem.

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