Automotive Air Conditioning Information Forum (Archives)

hey08 on Mon August 31, 2015 3:02 PM

Year: 1992
Make: buick
Model: roadmaster
Engine Size: 5.7
Refrigerant Type: r134a
Ambient Temp: 85

All components in this system are brand new. When the compressor is first engaged the readings start from 50-60psi low and 315-350 high. They then slowly drop to around 28-32 low and 190-200 high. A/c vents are ice cold. I used 8oz DEC PAG 150 from supercool.

I thought this was abnormal. I pulled the orifice and found a tiny bit of junk on it. Replaced with a new orifice, vacuumed for about 1.5 hrs sat for 30min no leaks, then charged it again with 2 cans of dupont 134a. Still the same result. Compressor is quiet and no abnormal noises.

85F and 60%humidity Is it normal for those pressures to be high at first then drop? Thanks for any advice!

Edited: Mon August 31, 2015 at 3:06 PM by hey08

GM Tech on Mon August 31, 2015 3:50 PM

Your clutch fan has morning sickness- 350 is too high on start up- put a garden hose to it to prove it is sluggish at first start-up- B-cars went to electric fans in about '96 model yr as I recall. Watch the air flow at start-up through the condenser as well. Air probably flows much better after a minute or two- that's why the pressures come down. It is not a big issue, unless you want it to be- I see it quite often on M-vans (Astros and Safaris). The a/c system needs immediate air across condenser while the cooling system can wait 15 minutes and the clutch fans are designed to "feel the heat" from the radiator- which just isn't there at start-up.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

AC_Doc on Mon August 31, 2015 3:54 PM

Sounds PERFECT TO ME!

Ever heard, "If it ain't broke don't fix it"

Quote
When the compressor is first engaged the readings start from 50-60psi low and 315-350 high.

Of course. The evaporator is swallowing a full load of heat from the cab. That raises the temperature (and pressure) of the evaporator.
This LARGE heat then must get dispersed at the condenser, so, of course, the High side pressure is going to go UP!

Quote
They then slowly drop to around 28-32 low and 190-200 high. A/c vents are ice cold.

After a minute or two of operation, the heat load settles down (and so do the pressures) to where they belong.
The lessened heat load to condenser also reduces the high side pressure.

PERFECT!


]Quote
I thought this was abnormal. I pulled the orifice and found a tiny bit of junk on it. Replaced with a new orifice, vacuumed for about 1.5 hrs sat for 30min no leaks, then charged it again with 2 cans of dupont 134a. Still the same result. Compressor is quiet and no abnormal noises.

Why would "ice cold operation" be abnormal?
You wasted a lot of time and effort and a load of refrigerant to get the SAME PREFECT results a second time.


Reminds me of a quote.
"If you think education is expensive, try ignorance" Derek Bok

Derek Curtis Bok is an American lawyer and educator and the former president of Harvard University.

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Sometimes you must accept things at faith value!

hey08 on Mon August 31, 2015 10:50 PM

I was just worried that those pressures could hurt the R4 compressor. I was confused when there was a tiny bit of junk on the orifice when i had pulled it out, cause every component of the system was brand new. Unless there was some junk in the new stuff. How possible is that? Guess I should just run it since its cooling good.

Cussboy on Tue September 01, 2015 8:32 AM

Quote
Originally posted by: hey08
I was just worried that those pressures could hurt the R4 compressor.


My experience with R4 compressors is that the R4 will "hurt itself" !!!

I had a 1988 Suburban with R4 and R-12, and a 1994 Suburban with factory R134a and R4. Maybe better without a dual-evaporator system...


Edited: Tue September 01, 2015 at 8:33 AM by Cussboy

hey08 on Wed September 02, 2015 2:57 PM

Because of the higher pressures at start up the high pressure switch cuts it off several times before the pressures go down. Is that normal for it to do?

Also this a/c hasn't been working for almost 2 years now and I finally got all new parts to put it back together. Its the been running for 9 days now. Why would there have been some junk on the orifice when the entire system is new? Thanks

mk378 on Wed September 02, 2015 3:20 PM

The high pressure switch should never trip in normal operation. If you're not going to replace the fan clutch you could wait until the car is in motion before turning the A/C on.

hey08 on Wed September 02, 2015 4:42 PM

The fan clutch should be fine it was just replaced a little under a year ago.

Edited: Wed September 02, 2015 at 4:44 PM by hey08

kapilamuni on Sat September 19, 2015 9:46 AM

Is your problem solved?

Regards

hey08 on Fri October 23, 2015 4:30 PM

Yes, I have solved my problem now and I think i might have a new one.

I don't normally drive this vehicle its a family vehicle and I had drove it today and noticed . The compressor is cycling on and off more than normal now.
Hooked the gauges up and the low side goes down and then it cuts off pressure goes up, compressor comes back on and it just repeats that cycle. The pressure when the system is off is about 75psi high and low.

I added 1 more can of 134a and it still sits about 75psi when system is off. I found that strange. Anyways that fixed the cycling on and off problem and low and high side pressure are normal when running. I do NOT see any evidence of leaks anywhere. The system originally required 50oz of r12. I had only charged the system with 24oz of 134a and now it should have 36oz in it.

So i think I might have undercharged the system to begin with, but it wasn't cycling like that before so its strange. Could ambient temp getting colder affect this? What is your alls opinion? Thanks again.

hey08 on Sun October 25, 2015 11:35 AM

I ended up adding a tad bit more refrigerant. I charged it 85% of the original 50oz of r12. Using a scale. I charged it to the best of my knowledge 5-6 more ounces.

Its 64F outside. Low side stays about 25psi and cuts off at 21.5. This compressor runs for about 30 seconds and off for about 15. When its on low or medium fan speed. Vent temps are at 38-40F.

So my main question is. Is it supposed to cycle more when the fan speed isn't on high?

Dougflas on Sun October 25, 2015 2:56 PM

when the fan speed is on low, the air moving across the evap is colder as it is in contact with the evap coil longer. At 64 *, there is not much of a load on the system to check performance. I would wait until the ambient is higher ( 80 ish) before checking capacity.