Automotive Air Conditioning Information Forum

AC blows cold at start up, after running for about 5 minutes the compressor seems to be slipping on the clutch.

You will need to post some initial pressure readings. Few things could cause this to happen.

I dont have the car in front of me at the moment. But immediately before the issue they were within range while running, AC on. What I recall is like 40-50 low side and around 190ish high side. 75-80 degrees out.

Vehicle is an 09 grand cherokee. With a kind of unknown AC past. The owner knows basically nothing about cars. He says the compressor was replaced a few years ago but AC never worked before or after, unknown as to why. First thing I noticed was the fuse was missing. Then I hooked up the gauges and it was pulling a vacuum on the low side. Took it all apart and found a stuck expansion valve, otherwise everything was spotless, but there was UV dye in it.

I still flushed it all out because who knows who worked on it or what they did. I flushed the lines, evap and condenser with AC system flush and let the compressor drip with the inlet/outlet holes facing down. I also blew the compressor out with shop air but did not use the AC flush on it. I blew out the parts I flushed with compressed air and replaced the expansion valve and dryer with new parts. The sticker on the car says 150cc (approx. 5oz) of PAG46, four seasons says 4.4oz. I put in about 4 ounces of oil, to account for any residual.

Pulled a vacuum on the system and it held overnight. Then I ran the vacuum pump for about 5 hours. I dont know if its my gauges or the pump but it never pulled more than about -28... never has (gauges sit at just slightly above zero not hooked up). System takes 24oz r134a. I refilled with 2x12oz cans of supertech r134a (it did not say anything about oil being added in on the can). After the first can the compressor started cycling. Sometime during the 2nd can it began to stay on. Air was blowing cold inside the cabin, then I noticed it wasn't, looked at the compressor and noticed the clutch was slipping and the compressor was doing about 1/4-1/2 spins slowly. I immediately shut it down. The compressor could still spin by hand (some resistance but could get it to turn with a gloved hand). I let the compressor cool. I then started the car again, AC on. Compressor kicked on and ran continuously for about 5 minutes. Then it happened again. After that I had to stop for the day.

I will report more accurate manifold gauge readings tomorrow.

Disclaimer - I'm not an AC professional.

I'd like you to measure if the AC clutch is still getting 12 volts positive after the AC clutch disengages. This is a safer and better test than CAREFULLY tapping the AC compressor drive plate with a wooden handle to see if it then engages.

In 2019, I had similar situation with my 1998 Nissan Frontier, and my AC clutch was still getting positive voltage when the AC clutch disengaged. I fixed that (still fixed today) by removing a shim to decrease the air gap; I didn't even need to remove the AC belt to do this, took less than half an hour.

Look at this link, start at Post #71 https://www.clubfrontier.org/threads/19 ... -4#replies

Ok, got back out to the vehicle. With the gauges unhooked and all valves wide open the low side reads at about +3-4psi. Put the gauges back on.the vehicle and checked the pressures.

Vehicle off, not ran at all today 78 both sides. 72 degrees F.

When I started the car I got a slightly different situation than yesterday.

AC on and the compressor cycles on and off like its low on refrigerant.

Here is a short clip of the gauge readings:

https://streamable.com/24zt74

GMBDguy wrote: Thu May 01, 2025 12:01 am I dont have the car in front of me at the moment. But immediately before the issue they were within range while running, AC on. What I recall is like 40-50 low side and around 190ish high side. 75-80 degrees out.

How much mileage has this vehicle logged?

If your recollection is correct, and with a low side of 40-50 PSI, the evaporator temperature will be at least 45°F and even higher, much too warm for any measurable cooling. The high side at around 190 PSI is about right for a 75-80°F ambient temperature, though.

GMBDguy wrote: Thu May 01, 2025 12:01 am Vehicle is an 09 grand cherokee. With a kind of unknown AC past. The owner knows basically nothing about cars. He says the compressor was replaced a few years ago but AC never worked before or after, unknown as to why. First thing I noticed was the fuse was missing. Then I hooked up the gauges and it was pulling a vacuum on the low side. Took it all apart and found a stuck expansion valve, otherwise everything was spotless, but there was UV dye in it.

It's very hard to tell whether a TXV is stuck (shut?). Normally, a TXV throttles the refrigerant and never actually closes completely. Usually, a vacuum reading on the low side means that the TXV is restricted by something, like desiccant beads from a defective receiver/dryer (R/D).

The UV dye isn't a problem unless someone put in much too much.

GMBDguy wrote: Thu May 01, 2025 12:01 am I still flushed it all out because who knows who worked on it or what they did. I flushed the lines, evap and condenser with AC system flush and let the compressor drip with the inlet/outlet holes facing down. I also blew the compressor out with shop air but did not use the AC flush on it. I blew out the parts I flushed with compressed air and replaced the expansion valve and dryer with new parts. The sticker on the car says 150cc (approx. 5oz) of PAG46, four seasons says 4.4oz. I put in about 4 ounces of oil, to account for any residual.

What did the flushing chemical look like when it came out the first time? Black or semi-clear? Any "glitter" (metallic particles) or plastic bits in it or in the compressor oil?
Since you flushed-out all the components and let the compressor drain out, I would have installed the full amount of PAG oil, 150cc (or 5.3 fluid ounces). Right now, I would guess that the system is about 1.3 fluid ounces short (not good for a system that holds only 5.3 fluid ounces) given that you installed about 4 fluid ounces of PAG. Incidentally, the under-hood decal always takes precedence over any other specifications, including those from Four Seasons.

Since we don't know the A/C repair history of the vehicle—and we also don't know whether the formerly replaced compressor was a rebuilt or new unit—I would have replaced the compressor with a new one, along with the condenser, which generally can't be effectively flushed, as well as the TXV and R/D, which you did. But IMHO, you completed only half the job by not replacing the compressor and condenser.

GMBDguy wrote: Thu May 01, 2025 12:01 am Pulled a vacuum on the system and it held overnight. Then I ran the vacuum pump for about 5 hours. I dont know if its my gauges or the pump but it never pulled more than about -28... never has (gauges sit at just slightly above zero not hooked up).

A few thoughts: Did you change the vacuum pump oil before evacuating the system? If not, the oil might have been contaminated with debris and moisture, which in turn could be why you didn't see a vacuum below about 28 InHg, even after five hours. Another factor is your location above sea level. The more elevation, the less vacuum that's possible.

In addition, you'll need to "zero" your gauges. Do this with the gauges disconnected from anything and the hoses off. Remove the soft white plugs in the face of the lenses, insert an appropriately sized screwdriver through the lenses, engage the adjusting screws, and rotate the screws until each gauge reads precisely "0". Replace the plugs. Or even better than a Manifold Gauge Set (MGS), use a micron gauge and ensure that it reads +/- 500 microns when you're done evacuating the system, again depending on your elevation.

From the MGS readings in your video, it appears that the system is low on refrigerant, which must be weighed-in for accuracy. The slipping clutch might be a byproduct of a low charge, bad compressor, clogged condenser, etc. The small cans probably don't have exactly 12 ounces net weight in them. In fact, I know they don't.

JohnHere wrote: Thu May 01, 2025 3:54 pm How much mileage has this vehicle logged?

212,000 miles

If your recollection is correct, and with a low side of 40-50 PSI, the evaporator temperature will be at least 45°F and even higher, much too warm for any measurable cooling. The high side at around 190 PSI is about right for a 75-80°F ambient temperature, though.

I could be entirely wrong on that number. It was getting late and I did not write anything down.

It's very hard to tell whether a TXV is stuck (shut?). Normally, a TXV throttles the refrigerant and never actually closes completely. Usually, a vacuum reading on the low side means that the TXV is restricted by something, like desiccant beads from a defective receiver/dryer (R/D).

I removed the TXV and attempted to blow through the metered small port and could not get any air flow at room temperature. I then dissambled the TXV and the pin was stuck shut. I could turn the TXV upside down and the pin would not fall free. After sitting on the bench a few days I took it apart again and it did fall free. Whether this was a previous issue before I got my hands on the car I do not know

What did the flushing chemical look like when it came out the first time? Black or semi-clear? Any "glitter" (metallic particles) or plastic bits in it or in the compressor oil?

T

he system was very clean. No evidence of dessicant, plastic, metal shavings or anything other than clean UV dyed oil. The compressor is a Four Seasons unit with a part number that is sold as a new compressor when I looked it up online. My suspicions (total theory here) is that the pulley bearing failied, a new compressor was installed and refrigerant recharged to see if they could get it to work (unknown shop did the work). It didn't work, then they quoted him a price to do it all correctly, as if the compressor puked and contaminated everything. He couldn't afford it and declined. The shop probably removed the compressor fuse to keep it from ever cycling on.

Since you flushed-out all the components and let the compressor drain out, I would have installed the full amount of PAG oil, 150cc (or 5.3 fluid ounces). Right now, I would guess that the system is about 1.3 fluid ounces short (not good for a system that holds only 5.3 fluid ounces) given that you installed about 4 fluid ounces of PAG. Incidentally, the under-hood decal always takes precedence over any other specifications, including those from Four Seasons.

I suspect that I did under oil, and that was something I thought about today before I read this post. I suspect my problem with the clutch slipping was due to low oil. The problems I had today was probably an additional issue due to reconnecting the hoses and losing some refrigerant and/or introducing so e air into the system.

I was always told "you cant get all the oil out. Always add slightly less". I am not an experienced AC guy, I have done a couple in the past but on both of those I used new compressors.

Today I added 1oz of oil to the yellow tube and about 2oz of refrigerant, measured on a small digital scale.

Since we don't know the A/C repair history of the vehicle—and we also don't know whether the formerly replaced compressor was a rebuilt or new unit—I would have replaced the compressor with a new one, along with the condenser, which generally can't be effectively flushed, as well as the TXV and R/D, which you did. But IMHO, you completed only half the job by not replacing the compressor and condenser.

In a perfect world I would have done that too, but also in a perfect world I wouldn't own and/or work on chrysler products The buddy I am helping out is poor and needs to sell this vehicle. He asked me if I could try to get the AC working on the cheap, as well as some other issues. So far he is only in about $140 in AC parts and supplies.

A few thoughts: Did you change the vacuum pump oil before evacuating the system? If not, the oil might have been contaminated with debris and moisture, which in turn could be why you didn't see a vacuum below about 28 InHg, even after five hours. Another factor is your location above sea level. The more elevation, the less vacuum that's possible.

In addition, you'll need to "zero" your gauges. Do this with the gauges disconnected from anything and the hoses off. Remove the soft white plugs in the face of the lenses, insert an appropriately sized screwdriver through the lenses, engage the adjusting screws, and rotate the screws until each gauge reads precisely "0". Replace the plugs.

The vacuum oil was not replaced but was clean in the sight lense. I have only used this vacuum pump one other time, a few years ago.

Thanks for the tip on the gauges. I will try that when I get back at this project.

Or even better than a Manifold Gauge Set (MGS), use a micron gauge and ensure that it reads +/- 500 microns when you're done evacuating the system, again depending on your elevation.

Yeah and one of those fancy shop style AC tools with all the push button features built in!

From the MGS readings in your video, it appears that the system is low on refrigerant, which must be weighed-in for accuracy. The slipping clutch might be a byproduct of a low charge, bad compressor, clogged condenser, etc. The small cans probably don't have exactly 12 ounces net weight in them. In fact, I know they don't.

I think I am going to zero the gauges. Re-evacuate the system. Double check for leaks. Pull a vacuum again for a couple hours and try this all over again. Now I am questioning how much refrigerant is in the system, since I have reconnected the gauges a couple times and I may have forgotten to purge the lines one time that I did it.

As for the oil, should I redrain everything and refill exactly? What about the oil in the dryer and other nooks and crannies? Where is the best place to add it? What about adding to an already charged system? Sone youtuber said you had to add half the amount to the compressor and have to the evaporator to keep the compressor from sucking a large amount of oil at once. He never elaborated how he added half to the evaporator, its not like you can just pour it in there without it going all over the place.

Learning about AC system work seems to be particularly annoying because the sheer amount of click-bait and wannabe youtube know-it-alls seems to add an extra layer of cloudiness to getting to the real knowledge.

Thank you for taking the time to help me out.