Automotive Air Conditioning Information Forum (Archives)

padgett on Sun March 04, 2012 2:31 AM

Year: 1986
Make: Vixen
Model: 21TD
Engine Size: 2.4L
Refrigerant Type: R12
Ambient Temp: 80
Pressure Low: 50
Pressure High: 120
Country of Origin: United States

This is a 1986 RV with a BMW engine, Bosch 0 140 903 217 compressor, rest is 1986 GMC Vandura with dual air: Oriface in front & POA in back. Compressor had leaking seals but no debris found. Know if using R-12 the proper amount is supposed to be 56 oz but is acting odd.

1) Replaced compressor with rebuilt original., dryer, and oriface. Replaced all Orings

2) Flushed twice

3) Pulled hard vaccuum for about an hour and held overnight.

4) Has proper mineral oil, spec amount added

5) Began adding R12 refrigerant. After 36 oz dryer pipe from evaperator felt cold. After 48 oz it did not feel so cold. Spec is 56 oz.

6) Getting about a 20 degree drop (58F at vent on high fan) which would be consistant with 8 oz low - however pressure when off is 80 psi, proper for R12 at 80F.

7) Oriface tube is warm at inlet, colder at outlet

8) Electric fan is running, good air flow and condenser feels cool to touch

9) When running dryer pressure (low side) is only dropping to about 50 psi at 1500 rpm with high side about 120 (uncertain about high side, need to check gauge).
Seems like low side should be much lower, Do not want to add more until resolved. Any idea why low side is so high ? (would expect more like 20-30 psi with slightly low R-12 charge).

Ideas welcome. Am an amateur but have done quite a few a/c compressor replacements & have proper tools. Could it be related to dual air ?

-------------------------
Many Carpets

Edited: Sun March 04, 2012 at 10:04 AM by padgett

mk378 on Sun March 04, 2012 10:39 AM

Did you flush properly (each piece separate), including disconnecting the TXV to flush the rear evap? Is it a new TXV? Is the TXV sensor bulb properly attached and insulated?

Proper procedure is to install a full charge then evaluate performance. Thinking about what should happen with a partial charge is over-thinking things.

padgett on Sun March 04, 2012 12:35 PM

Yes, each piece seperated and flushed independantly & new O rings fitted.

Saw no reason to replace rear valve, everything was clean even before flush.

Compressor is in back (is a pusher), rear air in middle, front is conventional GM with oriface tube/line next to dryer.

Is the rear air in series or parallel with front ? Are no gauge fittings there.

Reason I stopped here was because static pressure was correct but things did not seem right and wanted to ask - am not in a rush.



-------------------------
Many Carpets

Edited: Sun March 04, 2012 at 12:40 PM by padgett

bohica2xo on Sun March 04, 2012 6:13 PM

Static pressure is meaningless in the context of charge volume. You would have the same static pressure with12 ounces in that system.

You are still undercharged. The low side pressure reflects the collected heat from the dual evaporators. Your high side is low for all that heat, another indication of undercharge.

At 80f ambient & 1500 rpm I would expect to see 160+ psi on the high side, with both evaporator fans running. Get the spec charge in to it before it starves for oil.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

padgett on Sun March 04, 2012 7:05 PM

Added 12 oz can #5. Had minor leak at high side schrader so probably very close to 56 oz spec now & definately moving oil. Low pressure now 40 and high reading about 110. Am feeling more of a temp difference in the rear air POV lines than front (compressor in rear so gets to the rear air first) & about 20 feet of lines between compressor and where I am measuring.

Temp drop is about 20F with high volume fan on condenser. Air temp around 80F.

Do dual air systems read differentely from single ?

-------------------------
Many Carpets

Edited: Sun March 04, 2012 at 7:08 PM by padgett

bohica2xo on Sun March 04, 2012 9:34 PM

Two different systems with a common pump. It will never act like the average car system.

Test with all the doors & windows open, cabin fans on the highest speed settings. Engine speed 1500+ rpm. Run for 5 minutes to stabilize & take readings while at 1500 rpm or higher.

You have said "POA" a couple of times. Is there a POA in the system, or did you mean TXV?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

padgett on Sun March 04, 2012 10:03 PM

Sorry, I may be using the rong term from the 60's. This thingie: (expansion valve ?)

solvent used to flush (made for a/cs) discolored a bit.
Upper tube is warm, lower one is cold.

-------------------------
Many Carpets

Edited: Sun March 04, 2012 at 10:11 PM by padgett

bohica2xo on Mon March 05, 2012 10:33 AM

Yes, that is an expansion valve or TXV

B

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

JACK ADAMS on Mon March 05, 2012 12:03 PM

that is normal for the TXV to feel cold on one side and warm on the other. Its working, did this one get replaced? I work on one of these a wile back, kind of goofy set up but works. CCOT for the front and a TXV for the rear with a Bosch compressor. Need gauge reading at the coldest temp out the vent to see what may be happening if anything. Large BTU space to cool down for the size of the condenser and compressor set up.

Edited: Mon March 05, 2012 at 4:25 PM by JACK ADAMS

padgett on Mon March 05, 2012 12:53 PM

With 60 oz less some wasteage in (56 oz is spec for R12) it is reading 110-120 psi on the high side and 40-50 psi (varies) on low in front & getting 58 degrees (about a 20 degree drop) on high side. Not right. See first note for the complete specs but sounds like you have worked on a Vixen before. Everything is pointing to a low charge or possibly a too-open expansion valve (not replaced but seemed clean inside). Condenser is warm at top and cool at bottom, has a lot of air flow.

Be a while until I can get to the reclaimer but am tempted to just block off the rear air. Would these symptoms be consistant with a failing rear expansion valve ?




-------------------------
Many Carpets

mk378 on Mon March 05, 2012 1:19 PM

It could also be that your rebuilt compressor is a dud. Is that the "wing cell" unit?

Low side should drop if you turn off the rear fan. When the rear evap gets fully cold the TXV should close down, if it is working. You can also take the sensor bulb off of the line and put it in ice water, that should close the valve.

JACK ADAMS on Mon March 05, 2012 4:16 PM

Could be a bad TXV as well as a bad compressor. Not a big fan of the Bosch or rebuilds. The one that I worked on, I did a custom build mount for a Seltec Compressor. Didn't think about a repeat so didn't save any of the specs for building another one.

Edited: Mon March 05, 2012 at 4:24 PM by JACK ADAMS

bohica2xo on Tue March 06, 2012 8:43 PM

Full load test as I already outlined. Even a wide open TXV will work in that situation. You have an ambient of 80f, that should be enough for full load testing. No need to recover yet.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.