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How much oil and how much refrigerant?

steve48348 on Fri August 27, 2010 10:47 AM User is offlineView users profile

Year: 1983
Make: Chevy
Model: Van
Engine Size: 6.2 Dies
Refrigerant Type: R134
Country of Origin: United States

I have a 1983 Chevy Motorhome with an aftermarket A/C system, which looks very much like the the AMA14304-4192 kit from Arizona Mobile Air.
I have kept the evaporator. The original Sanden SD-508 compressor was replaced with a new Sanden SD7H15, the original tube and fin condenser was replaced with a new parallel flow type, which is approx. 25% larger.
I also put in a new expansion valve, drier and all new hoses.
The compressor came with 270cc oil in it, according to the label.

Question #1:
How much refrigerant should I put in?

Question #2:
According to the Sanden AC Compressor Service Guide, for a single evaporator system with a refrigerant charge of between 24oz and 40oz the correct oil charge is 135cc.
I'm pretty sure the required refrigerant charge falls somewhere within that range. So do I need to take roughly 1/2 of the 270cc of oil out of the compressor?

Thanks, Steve

bohica2xo on Fri August 27, 2010 10:58 AM User is offline

I would leave the 9 ounces of oil in it if the system is completely dry.

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.

HVargas on Fri August 27, 2010 11:42 AM User is offlineView users profile

If it were our kit, we would require 24oz for that system. I would start there and check your pressure's and report back with what you come up with.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: Arizona Mobile Air

steve48348 on Mon September 13, 2010 10:47 AM User is offlineView users profile

I got the system charged this weekend. I left the 9oz of oil in the compressor as bohica2xo suggested.
I filled from a 15lbs bulk container through the low pressure port. The compressor started pulling the refrigerant in and the system started working.
I used a 30lbs postal scale to weight the bulk container but it kept turning off on me in the process of charging and I had to repetitively re-weigh the container.
This is what screwed me up at the end. I have a feeling I got too much refrigerant in the system.
At this point I have about 32oz in the system instead of the just 24oz Adam had suggested to start out with.

The pressure readings are as follows:
Idle 20psi low side, 275psi high side
about 2000 rpm 10psi low side, 275psi high side
static after 5 minute engine off 140psi low side, 140psi high side

I noticed that when the compressor cycles off and then comes back on the belt slips for a few seconds causing a screeching noise before the compressor starts turning again.
Also, the condenser (used a new parallel flow type) only gets hot in the upper corner, right where the refrigerant comes in. The compressor head seems to be getting pretty hot.
It's too hot to keep your fingers on it while you can touch the compressor body. Not sure if it's normal that the head is that hot.
I do get cool air out of the evaporator.

The high static pressure and the compressor having a hard time starting up again makes me think I have overfilled the system. It should probably be more in the range around 70psi static.
Any help would be much appreciated.
Thanks everyone.

Tennessee_Timmy on Mon September 13, 2010 1:21 PM User is offlineView users profile

Quote
Originally posted by: steve48348


... The high static pressure and the compressor having a hard time starting up again makes me think I have overfilled the system. It should probably be more in the range around 70psi static. ...

70 psi static? not unless your ambient temperature is like 70*. 140 psi static was probably due to a hot engine compartment (or an ambient of 105* - 110*).

Even if you are overfilled by 8 ounces and you recover that, it won't affect the static pressure anyway.


-------------------------
Good Luck 2 ya,
Timmy

steve48348 on Thu September 16, 2010 9:02 AM User is offlineView users profile

Timmy you are right. Even though the ambient temperature wasn't too high that day the engine compartment had gotten pretty warm.
So the high static pressure was probably due the that fact.

I decided to hook up the gauges again and get temperatures also this time.
Here is what I have:

Ambient temperature 82*
Static pressure with engine cold 95psi/95psi

Opened doors, fan on high, temp. knob turned to max A/C, this A/C system is always in recirculation mode - it pulls the air from under the dash.

Started engine and let it idle for a few minutes before taking readings.

Idle readings
Pressure 20psi/165psi
Temp in front of condenser 75*/behind radiator 92* (radiator was still cold as thermostat hadn't opened yet - can't measure behind condenser as it sits right in front of the radiator).
Temp before evaporator 80*/after evaporator 32*

1500 rpm readings
Pressure 8psi/155psi
Temp in front of condenser 75*/behind radiator 107* (but radiator was getting warm so this temp is probably not accurate).
Temp before evaporator 80*/after evaporator 30*

When I turn down the A/C temp knob the compressor starts cycling. Everything seems to be working fine.
However, I do not have any idea as to where my pressure readings should be.
This vehicle initially had an aftermarket system with a Sanden SD508 compressor and ran with R12. In fact, it looks very similar to the system AMA is offering for the Chevy van.
I replaced the compressor with a Sanden SD7H15, installed a 15x27 parallel flow condenser, new expansion valve, all new hoses and dryer.
Only the evaporator unit is the original one.

When I charged the system I was attempting to put 24oz of R134 in but ended up with about 32oz as my electronic scale screwed me up.
I lost some refrigerant when the high pressure hose came loose on the gauge set in the process of removing the gauges (good thing I was wearing safety goggles).
Adam from AMA had said 24oz would be the initial target if it were in fact their system.

Can I get some comments on my actual readings shown above?
I feel the 8psi low side pressure at 1500rpm seems a little low.
Thanks everybody.

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