Working on fire engine AC (again)

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Dgreen
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Working on fire engine AC (again)

Postby Dgreen » Thu Jun 28, 2018 8:46 am

This truck is a 2003 E1. It has given us several rounds of trouble with the ac. Latest complaint was warmer than normal vent temps. Vent temp was in the low 50s on high idle and driving. Left it on low idle after driving around and vent temp went to 68. Pressures were 15 low side and 315 high. Ambient temp was 85. Pressure readings were at high idle. I changed he expansion. Valve yesterday thinking that would fix it. Idle vent temp was a little better 58, but pressures didn’t change much. 15 low side and 325 high. It was very humid and 95 degrees outside yesterday. The old expansion valve appeared clean.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Thu Jun 28, 2018 10:55 pm

With that high side check the condenser airflow.

Fan(s) OK? Somebody pluck a chicken in front of it when running? Overzealous cleaning with a pressure washer flatten all of the fins?
ice-n-tropics
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Re: Working on fire engine AC (again)

Postby ice-n-tropics » Fri Jun 29, 2018 2:41 pm

Preferred fire engine condenser is a Red Dot roof mount.
Hot air recirculation back into the front of the vehicle during long idle (especially with tail wind) causes high side spike and raises vent temp.
Feathers, especially Morning Dove, are better dealt with on the tailgate but skin on the breast result in more retained moisture.
hotrodac
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Fri Jun 29, 2018 6:26 pm

Actually Ice, you are closer than you think...

Both of those issues are from a nearby VFD. They killed a condenser on a rig with their brand new 4000 psi Diesel pressure washer.

They tried to kill a Mini-Split by plucking a bag of game birds up wind of the condenser. When it shut down they had no idea what the issue was, but called me to have a look because of the condenser kill the previous year...
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Sat Jun 30, 2018 3:30 am

The condenser is clean and the fins are in good shape. I guess the next step is to flush the condenser and put on a new drier. I was surprised to see that it wasn’t a parallel flow.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Tue Jul 03, 2018 5:17 am

Flushed the condenser yesterday and put on a new drier. Condenser was clean. I think I have too much oil in the system. The sight glass on the compressor was full. I think the oil level is only supposed to be half way up the glass. Drained out about 4 oz plus what was in the old drier. It’s working better. Vent temp stays in low 50s high side was 250 and low was 17 with engine on high idle. Outside temp was 88. Don’t understand why low side is so low? Oil level is at the top of the sight glass again.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Tue Jul 03, 2018 10:25 pm

Too much oil will absolutely hurt cooling & raise pressures.

Sounds like it still has a lot of oil in it if that TM31 compressor sight glass is full after draining 4+ ounces of oil.

I had a car recently that Firestone replaced a couple of compressors on that had an extra pint of oil in it. Messy, but no damage done.
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Wed Jul 04, 2018 3:43 am

Do you have any idea why the low side keeps running so low? I’m wondering if the location of the TXV isn’t causing this. It is mounted on the front of the evaporator. Wondering if it isn’t supplying enough refrigerant to the evaporator because it is in such a cold location?

Even when this truck was new, the ac wasn’t great. We have a 2014 model that is very similar to this 2003 and it will freeze you out on the hottest days.
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bohica2xo
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Re: Working on fire engine AC (again)

Postby bohica2xo » Wed Jul 04, 2018 9:44 am

Where & how is the TXV sensing bulb mounted?

Is the TXV internal or external equalized?

A picture of the TXV install might help
Dgreen
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Re: Working on fire engine AC (again)

Postby Dgreen » Wed Jul 04, 2018 4:54 pm

I have a pic where it mounts, but the file is to large.

It doesn’t have a sensing bulb going to the txv. There is a sensing bulb stuck in the evaporator coil that goes to an electronic switch. I think it cuts power to the compressor if Evap gets too cold. The txv is mounted up close to the evap fins. Air is drawn in vents to evap case and air flows across the txv and evaporator.

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