Fiat says "ouch," goes "thunk," and is now happy?

Andrew Owner/Technician Florida Posted   Latest  
Discussion
HVAC
2012 Fiat 500 Pop 1.4L (R EAB) 5-spd — 3C3CFFARXCT344135
Excessive High Side Pressure
Vacuum In Low Side
Missing Low Speed Fan Operation

Diagnostic Network,

I'm back again with questions. Grateful for past help received and would be grateful to receive more. If this post benefits anyone else (and I hope it will), better yet.

Please tell me what you think. I have (or had) a combination of symptoms and have yet to tie them to one root cause.

81k miles on this little Fiat. I just replaced the a/c compressor (installed a GPD) and receiver/drier.

Immediately after charging the a/c system, pressures were out of control. Pulling into vacuum on the low side and hitting 400-500 psi (or more) on the high side. No low speed fan operation.

I heard a *thunk* after a short amount of run-time. Immediately, the pressures stabilized, and low speed fan operation came back.

If I understand correctly, a/c requirement for low vs high speed fan operation is communicated via the transducer in the liquid line.

I can see a bad expansion valve, causing an excessive restriction, as explaining the excessive high side pressure and the low side pulling into a vacuum. The vehicle should have turned the fan on though.

However, I had added oil to the new compressor. This is (I think) a 2.7oz system. (I saw conflicting specs; the other was 1.7oz).

The old compressor barely gave up any oil. I put 2 oz in the new compressor.

Is it plausible, or reasonable, to be concerned that the compressor pumped oil up into the liquid line, in sufficient quantity to block the expansion valve and the schrader valve under the transducer?

As things stand now, this is the only theory I can think of that explains all 3 symptoms together. High side too high, low side in vacuum, and no low speed fan...All of these showed up together and went away together.

Since the *thunk** noise, the system has been running stably.

Today, at 100-105 deg F inside the shop, I saw operating pressures of about 180/35, with 45-47 from the left center vent (speed 2/air recirculating, LF window partially open, engine idling.).

I inspected the old dessicant for a rupture. No such trouble. If you have iATN access, here's a link: members​.​iatn​.​net/forums/read/ms…)

I'm curious about the concept here: of refrigerant oil interfering with refrigerant pressure against the transducer, and thus removing the schrader valve under the transducer. iATN link here: members​.​iatn​.​net/techmail/view…

I'd be grateful to receive advice and/or get educated. Questions welcome!

Thank you in advance.

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Paul Mechanic
Illinois
Paul
 

Did you spin compressor drive to distribute oil before installing? Sounds like oil slugging and possible compressor damage.

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Andrew Owner/Technician
Florida
Andrew
 

Hi Paul, Yes, I spun the compressor drive: on the car with the compressor in installed position, and prior to the compressor's first activation. Thank you.

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Glenn Owner/Technician
Texas
Glenn
 

Hello Andrew, I suggest it was a refrigerant oil flooding problem that temporarily created a blockage at the expansion valve. I have had this happen with both expansion blocks and orifice tube systems. The refrigerant does carry very small amounts of oil through the system, but it will not carry bulk amounts, that is when a flooding condition occurs. This flooding can happen in the fine…

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Andrew Owner/Technician
Florida
Andrew
   

Thank you, Glenn. I have erred and failed to provide a relevant piece of information. Please forgive me and let me know what you think. I did not fully comprehend, until after compressor replacement, that the old compressor had lost refrigerant through the relief valve. The car came in for a no a/c concern. I found that the compressor control button was not pushed, and the a/c turned on…

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David Owner/Technician
Alberta
David
 

Andrew, the blowing off of the relief should not destroy the compressor. It will lose your refrigerant though. That is one reason I asked this morning regarding why you changed the compressor in the first place. The root problem is likely still there if it was a blockage? You might be wise to change out the expansion valve and the trinary switch?

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Andrew Owner/Technician
Florida
Andrew
 

David, I just posted a reply to your response. I'd be grateful for your thoughts. Root blockage problem…an intermittent one? I won't say it's impossible, but if that's what I have on my hands here, it will be my first time. That I know of… Do you perceive that a severe restriction or blockage can come and go intermittently?

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David Owner/Technician
Alberta
David
 

Nope. The only intermittent restriction I imagine, that could come and go would be the expansion valve, maybe even a hose internal damage?. Really not likely though in this case IMO. But I can easily imagine a pressure sensor that does naughty things to do what you are experiencing. Not turning on the fan and system going to high pressure, blowing off a bunch of refrigerant and such.

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Glenn Owner/Technician
Texas
Glenn
 

Hello Andrew, A sticking expansion valve can be a tricky item to diagnose (and rare to occur) without repeat pressure spiking issues. In my experience expansion valve are not moody, they work, or they don't. If this were a much older R-12 system, then corrosion could be a factor, but it is not. Depending on how hard the valve is to access it might be a wise (peace of mind) investment to…

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Andrew Owner/Technician
Florida
Andrew
   

Hello Andrew, A sticking expansion valve can be a tricky item to diagnose (and rare to occur) without repeat pressure spiking issues. In my experience expansion valve are not moody, they work, or they don't. If this were a much older R-12 system, then corrosion could be a factor, but it is not. Hi Glenn, If I understand you correctly, you'd consider it possible that an expansion valve would…

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David Owner/Technician
Alberta
David
 

Andrew, you did not say why the compressor got changed so I am not as clear on this situation as I would like. And, I have never ever had the pleasure of working on one of these Fiat 500 wonders. Although the theory of oil interference has merit, could it be as simple as the trinary switch was giving a glitch as the expansion valve did not flow open when first started? I am thinking you…

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Andrew Owner/Technician
Florida
Andrew
 

David, I have let us both down by failing to provide a relevant piece of information. Please forgive me, and I hope this helps: The relief valve on the old compressor had previously lost refrigerant. I did not fully comprehend this until after compressor replacement. (Replacement was selected after pinpointing dye to the compressor body. Once I confirmed it had come from the compressor and…

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David Owner/Technician
Alberta
David
 

Andrew, the common thing here is the trinary switch. It could be the root of all the symptoms.

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Andrew Owner/Technician
Florida
Andrew
 

David, how could it cause (or contribute to) the low side pulling into a vacuum?

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David Owner/Technician
Alberta
David
 

The expansion valve staying closed due to all of the refrigerant coming at it and through?

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Andrew Owner/Technician
Florida
Andrew
   

David, I hope I'm not being a pain here. I am truly trying to understand. High pressure due to lack of airflow because of failed transducer control makes complete sense to me. I don't see anything causing a low side vacuum unless the expansion valve shuts (or gets close) or something else causes a major blockage on the suction side of the system. In your response, I'm not sure if you're…

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David Owner/Technician
Alberta
David
 

Andrew, I find it helpful to think of how that system operates. What is it that puts the pump on and off due to what situation is where I am looking at. What is it that closes the expansion valve or opens it? Probably that may help you figure this rascal out to your own satisfaction.

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Jon Owner/Technician
California
Jon
 

All of your oil was in the compressor… The older Toyota Sequoias had a design flaw in them where all the oil would drain into the compressor if it was parked at certain angles. They would act the same way as your Fiat. The customer complaint would be an intermittent “thunk” on start up. It took us forever to figure out what was going on. Toyota made design changes and they use to provide a…

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Andrew Owner/Technician
Florida
Andrew
 

Jon, Thank you for this reply. You have provided helpful information that I'm grateful to have. How far do you go in adding oil to the driers, Jon?

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Jon Owner/Technician
California
Jon
 

It depends on the size of the system. I will usually put 2-3 oz's in the receiver/dryer.

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