Working on fire engine AC (again)

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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Sun Jul 15, 2018 4:47 pm

The compressor on that truck easily makes 15,000 btu/h by 3000 compressor shaft RPM. It is a 323 cc/rev unit.

That valve is for a 1978-85 Porsche 928. An R12 car with a little Nippondenso 6E171 compressor. That valve also crosses to Dodge K car, Renault LeCar Dodge mini vans... Nothing with big systems.


Can that valve be installed backwards? or is the liquid line thread different on the in & out?
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Sun Jul 15, 2018 6:07 pm

Valve can only go one way.

Friend at the parts store sent this.
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Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Tue Jul 17, 2018 1:02 pm

I have a little more info to add to this puzzle. About a year ago we put on a new compressor. I found the expansion block that got changed when the compressor got changed. It has a Parker number on it. 329-412 It also has R-134A printed on the block. I compared it to a Four Seasons expansion block like what is currently installed on the truck. The hole where the refrigerant enters the block is larger on the one with the Parker number. The Four Seasons doesn’t say R-134A on it.

Is this possibly the reason for the poor cooling and low suction pressure?
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Re: Working on fire engine AC (again)

Postby bohica2xo » Tue Jul 17, 2018 3:43 pm

There it is. The wrong TXV.

The CV on the parker valve is about twice that of the 4 seasons replacement.

Twice as much refrigerant mass per minute in to the evaporator.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Thu Jul 19, 2018 1:37 pm

I looked up both expansion block part numbers on the internet. Both say for R-12 and R-134a. I adjusted the valve today and no change. The low side was 11 psi and vent temp 50. The outlet pipe of the evaporator was frosting up.
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Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Tue Jul 31, 2018 2:32 pm

I found some info on stationary hvac with expansion valves and the problems caused by too much oil. I’m wondering now it that isn’t the reason for the unsatisfactory cooling we’re getting in our engine? I think it still has too much oil.

Also, the compressor clutch self destructed again last week. New clutch arrived today from AC Kits. Going to remove more oil when we change the clutch.
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Re: Working on fire engine AC (again)

Postby bohica2xo » Tue Jul 31, 2018 7:44 pm

Is that compressor still accumulating oil? I thought you had things cleared up with the oil overcharge.

Yes, too much oil hurts cooling.

But a TXV that can't pass enough refrigerant is how you get high suction pressures at the evaporator when there is not much air moving over it.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Wed Aug 01, 2018 5:45 am

Last time I drained the oil down to where the sight glass was about 3/4 full. My thinking was some oil would settle in the new drier. No oil was added to the new drier before it was installed. After it ran a while, the sight glass was full again. My plan is to recover the charge so I can change the clutch on the workbench. Will drain the oil down to where it’s half way up the sight glass. Should I try to remove excess oil from the drier or can too much oil ruin them?
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Wed Aug 01, 2018 6:39 am

I may also flush the evaporator and condenser a second time. I’m concerned they may be oil logged now.
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Re: Working on fire engine AC (again)

Postby bohica2xo » Wed Aug 01, 2018 6:49 am

Wow. That thing is seriously over oiled.

I would at least dump the excess oil from the dryer & reset the sump to 1/2 sightglass. Then run it for a few minutes & check the sightglass again.

Do you have the capacity to do a refrigerant flush on the evaporator?

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