Abnormal high side pressure on AC

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Abnormal high side pressure on AC

Postby ofelas » Wed Aug 05, 2015 10:14 am

Hi, 91.5 truck with all 93 AC pieces -

Alrighty. I did the following -

New gaskets & o-rings everywhere.

5oz oil in the compressor, 2oz in condenser, 1oz in evaporator & 1oz in drier.

Nitrogen in the system at 300psi and it held for almost 2 hours - no drop in pressure at all.

Ran 26psi vacuum on the system and it held for 2 hours.

Sucked in 40oz of R12 with the compressor cycling at 1300rpm + Max AC + blower fan on high.

Compressor OFF: 50psi low side and 220psi high side
Compressor ON: 25psi low side and climbs in a few minutes to 450psi high side.
Faceplate vent temperatures - 46-50 F

Raising the rpm to 1200-1300 turns the compressor OFF and high side drops almost instantly to 200-250psi

Why am I getting such high side readings, and is it normal for the compressor to be ON constantly until it de-clutches at 1200rpm?

Possibly fan clutch not enga
R12 = liquid bilit
ofelas
fuel screw!!!!
 
Posts: 76
Joined: Mon May 04, 2015 4:02 pm
Location: ON & TX

Re: Abnormal high side pressure on AC

Postby BC847 » Wed Aug 05, 2015 2:12 pm

ofelas wrote:Hi, 91.5 truck with all 93 AC pieces -

Alrighty. I did the following -

New gaskets & o-rings everywhere. Nice!

5oz oil in the compressor, 2oz in condenser, 1oz in evaporator & 1oz in drier. I've not studied the FSM or sticker under the hood but I expect you're well in the ballpark regarding the quantity of oil. Spreading around the oil isn't necessary as I expect you know it'd get around the refrigerant circuit with normal operation.
- Did you remove all the original oil?


Nitrogen in the system at 300psi and it held for almost 2 hours - no drop in pressure at all. Good.

Ran 26psi vacuum on the system and it held for 2 hours. I expect you mean 26"mg (26 inches mercury vacuum). While that's much better than nothing, a digital micrometer would have told the tale of any possible leaks but would also include evidence of moisture in the system. The two-hour runtime may very well have removed possible moisture (I think I'm preaching to the choir here). LOL!

Sucked in 40oz of R12 with the compressor cycling at 1300rpm + Max AC + blower fan on high. Again, I'm assuming that's the correct quantity. The proper way to instill the new refrigerant in the evacuated/dehydrate circuit would have been to release all the liquid refrigerant of the high-side of the system . . . with the system OFF. Having instilled all it would take, then start the system and allow the balance of the refrigerant to be drawn into the suction side of the system as a VAPOR.

Here's hoping the compressor wasn't damaged by the oil being washed out / diluted, never mind the valves being hurt via possible slugging of the compressor.


Compressor OFF: 50psi low side and 220psi high side Assuming the system was OFF, for say, ten minutes, I'm concerned the evaporator pressure didn't equalize with the high-side. Do our TXV's have the external equalizing tube (built in of course)? If it does, that would explain your readings.
Compressor ON: 25psi low side and climbs in a few minutes to 450psi high side. The words you have typed here say the suction pressure started at 25psig, and rose to 450psig? Or did you run the two different readings together?
Faceplate vent temperatures - 46-50 F With what return-air temperature?

Raising the rpm to 1200-1300 turns the compressor OFF and high side drops almost instantly to 200-250psi. OK. A number of things can alter said reading.

Why am I getting such high side readings, and is it normal for the compressor to be ON constantly until it de-clutches at 1200rpm? Remember, the compressor is nothing more than a VAPOR pump. It's only going to move so many CFM of vapor per minute at a given RPM, incoming vapor density, etc. With a return-air temperature of 85*f, one may very well be boiling off enough liquid refrigerant in the evaporator such that, at a low pump RPM, the pump may run continuously. At a higher pump RPM, the same load on the evaporator may be low enough to have the pump cycle. Nothing out of the ordinary there.

Possibly fan clutch not enga


That 450psig reading is WAY too high ref" http://www.refrigerants.com/pics/ptchart.pdf
- When was the last time you cleaned the condenser coil (high strength detergent followed by a strong pencil stream of water flushing)?
- Is the engine coolant fan clutch whacked? With the engine well heated and the fan moving hot air, shutting down the engine, can you easily spin the fan and have it continue spinning (indicating the clutch is NOT engaged)?
- Is 40 ounces of liquid R12 the correct factory spec charge?

I apologize if my questions are sorta rough and straight to the point, I spend all day supervising the HVAC shop for North Carolina's largest county school system. It's been a long day . . . . all week.
David

1993 12mm VE Fueled W250 CC, Green
12.67 @ 103.35
Your basic farm truck ;)
BC847
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Re: Abnormal high side pressure on AC

Postby ofelas » Wed Aug 05, 2015 5:02 pm

Yes, I meant 26hg vacuum not psi.
I did dump in the 40oz with both hoses unvalved, I guess it equalized.
This morning while idling in traffic - there was a loud hog squeal from the engine bay and mist came through the vents and hood gaps. I assume it was the high pressure relief valve on the compressor venting.
AC worked normally when I drove the truck again this afternoon.Compressor cycles on and off normally now and my vent temps are 40F with this afternoon being 85F with 69% humidity. Pressures are good as per the FSM.
Maybe the compressor burped an air pocket on the discharge side?
**** Dodges.
When I'm in GA next I'll bring a jug of R12 and gauges with me to NC - I'll even bring some real BBQ to relieve you of that vinegar based stuff :-D
R12 = liquid bilit
ofelas
fuel screw!!!!
 
Posts: 76
Joined: Mon May 04, 2015 4:02 pm
Location: ON & TX
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Re: Abnormal high side pressure on AC

Postby ofelas » Wed Aug 12, 2015 5:21 pm

Got mine finally fixed.

My damn fish scales were bad; there was a low charge in the system.

Vacuumed the R12 out, refilled 38oz R12 on a digital stand scale.

Vents are blowing 36F air with ambient of 87F and 88% humidity.

Pressures are 36psi low and 195 high.

Compressor cycles 4 times a minute for 10-12 seconds a time.

New clutch went in anyway...holds a dollar bill against the front grill even while the fan is freewheeling at idle. Old clutch didn't do that.
R12 = liquid bilit
ofelas
fuel screw!!!!
 
Posts: 76
Joined: Mon May 04, 2015 4:02 pm
Location: ON & TX
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Re: Abnormal high side pressure on AC

Postby BC847 » Wed Aug 12, 2015 6:58 pm

That would explain the abnormally high pressures.
Glad you got it fixed. :)
David

1993 12mm VE Fueled W250 CC, Green
12.67 @ 103.35
Your basic farm truck ;)
BC847
Administrator
 
Posts: 2203
Joined: Wed Jan 03, 2007 5:22 pm
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Re: Abnormal high side pressure on AC

Postby ofelas » Wed Aug 12, 2015 7:09 pm

There go my fish tales.
R12 = liquid bilit
ofelas
fuel screw!!!!
 
Posts: 76
Joined: Mon May 04, 2015 4:02 pm
Location: ON & TX
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