AC Pressure drops to zero when clutch engages

[jmonica]

Hey Guys, I'm not sure I even want to open this can of worms. I don't know enough about A/C systems to now exactly what I am doing. Just what I've read on here. I replaced the A/C compressor about 1.5 years ago along with everything else I was supposed to replace. I flushed the system and really tried to do everything by the book. The AC blew kind of cold. Then I parked the vehicle for a year.

Skip forward to today. The AC clutch wasn't engaging. I jumped the relay and the clutch engaged so I tried charging it, which kind of made it work. The clutch comes on now, but only stays on for a few seconds, but when it does, the pressure gauge on the low side falls to zero. As soon as clutch disengages, pressure goes back up. So dilemma one is I have no way of knowing how much refrigerant to add because the gauge goes to zero when clutch engages which is when the can says that I should check that the pressure gauge is in the green.

It definitely took about a half a large can of R134a but obviously I have other issues and it doesn't even try to blow any cold air out the vents at this point.

I might have more info if I could find the darn Blue and Red Gauge set that I bought a year or two ago, but it's mysteriously disappeared.

Thanks in advance and hope al of you guys are doing well!

 

[TJBaker57]

Hey Guys, I'm not sure I even want to open this can of worms. I don't know enough about A/C systems to now exactly what I am doing. Just what I've read on here. I replaced the A/C compressor about 1.5 years ago along with everything else I was supposed to replace. I flushed the system and really tried to do everything by the book. The AC blew kind of cold. Then I parked the vehicle for a year.

Skip forward to today. The AC clutch wasn't engaging. I jumped the relay and the clutch engaged so I tried charging it, which kind of made it work. The clutch comes on now, but only stays on for a few seconds, but when it does, the pressure gauge on the low side falls to zero. As soon as clutch disengages, pressure goes back up. So dilemma one is I have no way of knowing how much refrigerant to add because the gauge goes to zero when clutch engages which is when the can says that I should check that the pressure gauge is in the green.

It definitely took about a half a large can of R134a but obviously I have other issues and it doesn't even try to blow any cold air out the vents at this point.

I might have more info if I could find the darn Blue and Red Gauge set that I bought a year or two ago, but it's mysteriously disappeared.

Thanks in advance and hope al of you guys are doing well!

Keeping it simple... you have a leak somewhere. If the leak was such that ALL refrigerant leaked out then at a minimum you need to again evacuate the system with a vacuum pump before recharging. Best practices would say the leak must be found and repaired. As for how much to add have a look at the sticker under the hood for the total charge in ounces. That is the maximum.

My guess is that you have a significant leak. To lose enough refrigerant such that the system low pressure switch prevented compressor operation after a year sitting idle suggests a significant leak.

 

[jmonica]

Thank Ypu for your reply. I have a confession. When I replaced the compressor and recharged it, it never really got that cold. Just cool. I hooked up the gauge again and I had in fact overcharged it. I left it alone when I parked it.
Once I started it back up and summer came, I removed some of the refrigerant. I don’t have equipment for that at home so I wrapped it in a wet rag and let some of it out. It’s the only way I could think of evacuating some of it without letting it go into the atmosphere. Anyway I was afraid I may have emptied too much and so started this whole recharging thing at the start of this thread. So at this point I guess my best bet is to buy a mew set of gauges and test for a leak to rule that out.
Thank You again for your great reply! I appreciate it

 

[TJBaker57]

If you have an OBD2 adapter you should be able to read the AC high pressure from the PID for that parameter. That would sidestep the lost gauge set for the moment. And to tell the truth I think reading the high pressure under actual driving conditions is a far superior way of 'tuning in' a charge when evacuating and recharging by weight is not a readily available option.

I noticed you have not mentioned the evacuation with a vacuum pump designed for the purpose when the compressor and other parts were replaced. It cannot be be overstated that this step is imperative to proper AC system recharge after the system has been opened OR allowed to discharge. Nothing else can take the place of this step. There are no tricks or workarounds.

FWIW, the wet rag changed nothing, it still went to the atmosphere in the very same manner. I think most of us have 'had' to do this at some point.


In your current shoes, if the system was properly evacuated with an hvac vacuum pump when the compressor was changed, and when you released some of the charge it never went down to no pressure, I think I would add enough refrigerant, with dye, to get the system operational and observe over time. Err to the side of undercharged. AC systems are a real case of more is not better when it comes to the state of charge.

 

[jmonica]

Thanks so much for your reply. I am going to work on it this weekend. I didn’t realize the OBDII adapter read the AC high pressure level so that’s good news. I will report back and with any luck I won’t be climbing out of the vehicle soaking wet from sweat soon! Thank You again and have a great holiday!

 

[TJBaker57]

Thanks so much for your reply. I am going to work on it this weekend. I didn’t realize the OBDII adapter read the AC high pressure level so that’s good news. I will report back and with any luck I won’t be climbing out of the vehicle soaking wet from sweat soon! Thank You again and have a great holiday!

Just in case you don't have the PID setup to use in Torque Pro or equivalent...

mode & pid =22114401
header=Auto or 6C10F1(for non-canbus systems)
Equation=A*1.83-14.7