Automotive Air Conditioning Information Forum

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?

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

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???

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.

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.

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?

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.

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

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.

One thing I'll add as I just went through something very similar (you can check my thread) is that even though the line may feel really cold it's hard to really gauge by feel if it's cold enough. I thought mine was ice cold but it was really only 70 degrees. It was just so hot outside and in my garage it probably made it feel colder than it was. My infrared temp gun couldn't get an accurate temp (was indicating about 90) but my meat thermometer have me an accurate reading of about 70 quick is what my vent temp was about. I think if you can get an accurate reading of this line going into your evaporator it's a good test as it seems like your pressures are off a little instead of digging through your dash for a blend door issue (not saying it can't be that but I'd work on getting the pressures right and the low side line temperature right first off is not already)

I had similar readings as yours and even swapped out compressors like you but mine ended up being the expansion valve (I installed a new one as well but I guess it was bad out of the box). I was getting vent temps 60 to 70 and now get 45 to 50. That 10 to 15 degrees makes a huge difference)