A/C diagnostics questions

[ck80]

I've gotten the pleasure (?) of trying to figure out what happened with the A/C on my wife's 2016 v6.

The history: nornal usage, no issues, worked when parked one night in cold conditions just below freezing, then the next day no a/c.

What I've done to check:

Fuses: both good, engine bay & pass footwear.

Clutch Relay: did the swap with horn relay trick. Both relays work in the horn slot, so, either one in the a/c clutch slot should.

Compressor: clutch turns free with normal resistance by hand, but, does not engage from dash control. Remove the relay and jump with pliers and the clutch engages.

Pressure switch: system recognizes the pressure switch and is getting some signals. Fans turn on when plugged in, and, turn off when unplugged.

R134a: system has pressure. If anything, too MUCH pressure. As I've played around testing the components, when hooked to the gauges if I jump the clutch relay the high side pressure rises and keeps going, reading north of 450 PSI when I back off out of fear of rupture.

When the clutch is jumped the air coming out of the vents DOES change from being warm to being normal cold.

The system has NEVER been apart or serviced since new, still has the factory charges of oil and r134a. Never been topped off, and, today was the first time it's had gauges on it aside from anything that may have been done pre-delivery.

When the caps were removed to install the lines to the gauges, the high pressure side actually was pressurized under the cap to where it actually launched free when removed- to the extent that indicates high pressure had been an issue and some escaped the valve.... not sure.

Tried jumping the pigtail to the pressure sensor, and, made no changes to how things worked... or should I say didn't.

I presume the pressure sensor has a schrader valve under it, and, thus could be unscrewed and changed without evac-ing the system correct?

Aside from all that, not sure what else it may be. Had it had the evap leak people talk about I'd assume it wouldn't blow cold when the relay was jumped with needle nose pliers.... right?

Any input would be appreciated, thanks.

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[jloshotz]

One thing I can advise, when you jump out the Compressor clutch relay, I’m sure this doesn’t allow the condenser fans to energize, so don’t jump the gun and bleed refrigerant off. Also at that high a head pressure, it also won’t evaporate through the txv into the evap, so it won’t feel very cold at all. The high pressure side will climb rapidly without condensing, this sounds normal. As far as the pressure sensor having a shrader depressor and a shrader underneath it, don’t assume that it does. I’ve seen plenty that will, and others that don’t. And it WILL hiss either way, due to the schrader still being depressed if it actually has one. Until it doesn’t and it’s too late at that point. I would check the system charge (you hadn’t mentioned what the low side pressure was reading) with the Low pressure switch jumped out, and both high and low side gauges connected. This way should also command the condenser (rad) fans on. Then you can see that the low side starts pumping, but not low or into a vacuum. Too low of a back pressure (low side) with a close to normal high side, you may have a restriction, blocked txv or drier. Running pressures on a 75° day should be high side optimally around 125-200 psi, low side should run between 20-40 psi. Once you proof this out, then you can see where your control voltage is being interrupted. E.g. Hp switch, Lp switch, or signal from elsewhere. It sounds a bit daunting, and I hope this all makes sense to you. I’ve repaired commercial refrigeration/HVAC for 35 years so this troubleshooting comes somewhat natural to me, cars are a bit of a different animal, as there are a lot of electronics in play these days also. Hopefully some of this can help you get started with the troubleshoot. I need to do the evap in my 2016 at some point, and that should be interesting to say the least. If you have any questions about anything I e suggested here, I’ll do my best to help. Good luck

 

[ck80]

One thing I can advise, when you jump out the Compressor clutch relay, I’m sure this doesn’t allow the condenser fans to energize, so don’t jump the gun and bleed refrigerant off. Also at that high a head pressure, it also won’t evaporate through the txv into the evap, so it won’t feel very cold at all. The high pressure side will climb rapidly without condensing, this sounds normal. As far as the pressure sensor having a shrader depressor and a shrader underneath it, don’t assume that it does. I’ve seen plenty that will, and others that don’t. And it WILL hiss either way, due to the schrader still being depressed if it actually has one. Until it doesn’t and it’s too late at that point. I would check the system charge (you hadn’t mentioned what the low side pressure was reading) with the Low pressure switch jumped out, and both high and low side gauges connected. This way should also command the condenser (rad) fans on. Then you can see that the low side starts pumping, but not low or into a vacuum. Too low of a back pressure (low side) with a close to normal high side, you may have a restriction, blocked txv or drier. Running pressures on a 75° day should be high side optimally around 125-200 psi, low side should run between 20-40 psi. Once you proof this out, then you can see where your control voltage is being interrupted. E.g. Hp switch, Lp switch, or signal from elsewhere. It sounds a bit daunting, and I hope this all makes sense to you. I’ve repaired commercial refrigeration/HVAC for 35 years so this troubleshooting comes somewhat natural to me, cars are a bit of a different animal, as there are a lot of electronics in play these days also. Hopefully some of this can help you get started with the troubleshoot. I need to do the evap in my 2016 at some point, and that should be interesting to say the least. If you have any questions about anything I e suggested here, I’ll do my best to help. Good luck

This is what I would get with the condenser fans on as a baseline:

As you stated, pressure would continue to climb on the high side, and, I was afraid of the pressures it was pushing already, although I did end up letting jt climb somewhat closer to 500 the first two timrd.

However, this was the consistent pressure reading across several test ctimes, as a starting point. The car/engine was warm as in up to temp, as we drove it over to where were trying to diagnose. Outdoor temperature was 74 degrees, and, 51% relative humidity, with front end of car being shaded.

Thanks for your input and any insight as we go forward, it's much appreciated.

 

[K4fxd]

My educated guess is the dryer has ruptured and plugged the condenser.

 

[jloshotz]

Do you live in or operate the car in overly dusty conditions? Try hising down the condenser (avoiding the fan motors as best as possible) to see if the head pressure drops, and be sure the fans are drawing through the condenser. DC motors will spin backward if polarity has been changed, be sure they aren’t “pushing” or attempting to push rather than pull. Those pressures almost seem like air was introduced into the system though, did you purge the gauge hoses of air? Just asking, because each hose is capable of holding an ounce or two of air, and if your charging handles weren’t seated when you hooked to the service ports, you may have introduced air which is a non-condensible…..which would lead to a high head pressure. Just tossing it out there.

 

[K4fxd]

Those pressures almost seem like air was introduced into the system though,

No, those pressures act like the system is plugged.

 

[jloshotz]

Is there really enough desiccant in that drier to plug the most likely 3/8” condenser tubing?? I could see the txv orifices, but the actual condenser?? Educate me please

 

[jloshotz]

If it was plugged (at any point) that back pressure would pump down into a vac but fast. Just saying 🫡

 

[K4fxd]

Is there really enough desiccant in that drier to plug the most likely 3/8” condenser tubing?? I could see the txv orifices, but the actual condenser?? Educate me please

Oh yes there is. I've seen 3 Gen 2's do this already, mine was one.

 

[jloshotz]

If you’ve seen it, and had personal experience, then definitely good advice

 

[K4fxd]

If it was plugged (at any point) that back pressure would pump down into a vac but fast. Just saying 🫡

Eventually it will pull a vacuum on the low side unless the clutch starts slipping. Which is what mine did.

 

[jloshotz]

Interesting….hopefully the OP doesn’t have this issue, I would never have checked that FIRST. But if this is a common (or even uncommon yet known) problem, damn. Were you able to blow the condenser clean, or was it straight replaced? Any other components affected? Curious how the repair process went. Sounds nightmarish!

 

[K4fxd]

I ended up having to replace the condenser and compressor. Blew the lines clean and has been working fine since. Mins plugged slowly it would work then not work. When I figured it out I saw smoke coming from the compressor clutch before it tripped out.

I thought it needed a clutch till I hooked gauges up to the system. I might have been able to blow out the condenser but why take a chance on blowing another compressor.

 

[K4fxd]

For the OP's car I would un hook the condenser and see if it is plugged.

 

[jloshotz]

Yeah, I agree with that replacing it is well worth not risking a new compressor for sure. Let’s see where the OP goes with this. Thanks for the experienced input. Everything is helpful

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