Automotive Air Conditioning Information Forum (Archives)

BG1 on Thu July 29, 2010 6:03 PM

Year: 1990
Make: Chevy
Model: 1/2 ton pick-up
Engine Size: 5.7
Refrigerant Type: R134
Ambient Temp: 90-95
Country of Origin: United States

What does it tell you when the high pressure side drops alot when you spray water on condenser? I am having trouble getting it to work correctly. It is a 1990 Chevy truck that was R12 and now has R134a, I flushed the evaporator, condenser, ran new oil thru the compressor to clean it out, replaced the orifice, replaced the accumulator and blew out the hoses. I also put in 7-1/2 oz of ester oil and 31 oz of r134a and a new orifice (blue). The old orifice was not clogged up and I did not notice any restriction on the evaporator or condenser when I flushed them out. I filled the gap between the condenser and the radiator with foam to help the air flow and changed the fan clutch to a new one. The pressures (low 35-39) with the (high 275-300) with outdoor temp 95 degrees and the dash vent 54. With water over the condenser
(low 23) and (high 170) vent temp 46. Road test 50 mph (low 25-30) and (high 235-250) vent temp 46-50.
The system was working pretty decent before R134a leaked out because of a bad o-ring. It has the picolo condenser that is between the tube and fin and the parallel condenser (I think the names are correct?)

1stbscout on Thu July 29, 2010 7:52 PM

Water over the condenser is considerably cooler and does a better job of cooling the refrigerant. The pressure will change with the extra cooling. Consider that the temperature of the water is probably 65 to 70 degrees. As compared to an air temp of 95. This is the first step in understanding.

If you are going to do a "water" test you need to just mist the core. The idea is not to change the temp by much just to augment the cooling.

Personally the high side seems a slight amount high to me. @ 95 ambient I rarely see high side pressures above 275 and normally they are a few pounds less. Down in the 265 range.

What temperature is the outlet of the condenser running at with the vehicle idling? This will tell you a huge amount about how the condenser is performing. Measure the inlet temp and the outlet temp. The difference tells you how efficient the condenser is. The closer to ambient the outlet is the better the system will cool and the lower the high side pressure will be.

bohica2xo on Thu July 29, 2010 9:17 PM

Pressures look about right for a conversion. the road test looks fine.

Water will drop the pressures quickly, but yours do not look out of line for that vehicle @ 95f & idle.

Run the full load test. Doors open, cabin fan on highest speed. Run the engine rpm up to 1500, and hold it there for 5 minutes. Check the pressures while the engine is still at 1500 and post them.

B.

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"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.

BG1 on Thu July 29, 2010 9:20 PM

Does it sound like its very far from where it should be? Is there any thing else I can do to make it work better? Or is this about what I should expect with R134a? My other choice would be to go back to the R12. Stopped at an intersection the pressures go and also my engine temp. Is there any thing I can do to keep these down?

98audiA4 on Thu July 29, 2010 9:37 PM

I'm no expert but I did stay at a holiday inn express. All the performance charts I've seen in various car factoryh service manuals would agree 46 vent temp iin 95 degree heat at speed is a pretty good temp to be at.

bohica2xo on Thu July 29, 2010 9:55 PM

Make sure the air path through the heat exchanger stack is clean. Bugs, dirt, road grime, etc. can plug the fins below the surface, and make it run hotter than normal.

Sometimes a conversion needs more airflow. Adding an electric pusher fan in front of the condensor can help low speed performance.

Clean the condensor & radiator first. Start with a cold condensor & radiator. Sparay a strong surfactant like Simple Green or ZEP Citrus deep into the fins. Flush it out with a garden hose. You may be surprised at how much filth comes out.

B.

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"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.

iceman2555 on Fri July 30, 2010 4:45 PM

The 'pic' condenser was not available OE for this vehicle. Has the condenser been changed? Was this part of the retro fit procedure? The 'pic' condenser is a 134a condenser and should allow for a full refrigerant recharge. One issue with the 'pic', is that the some of the aftermarket units are actually brass and copper as opposed to the OE unit constructed of aluminum. The brass and copper units do not transfer heat was well as the aluminum units. Check the construction of your unit.
The additional cooling offered by a supplemental electric fan is a good option to reduce temperatures.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

BG1 on Fri July 30, 2010 7:15 PM

I might have spoken to soon on the type of condenser I have. I was talking to someone who has worked on these and asked me to describe it to him and he said he thought it was a picolo type condenser and I have not found any good pictures to tell me what type it is so I may be wrong.
The one in my truck has 2 header tubes on the passenger end of the condenser and the other end has loops on it, and going thru the middle the tubes are staggered and they are 6.74mm outside dia. So what do I have? Thanks

BG1 on Fri July 30, 2010 7:30 PM

I did the "Full Load Test" and the results were (23-26 low side) and (260-275 high side) vent temp 44-50
outdoor temp 90 degrees this was with the windows down doors open. With the windows closed and vents open the results were (25-30 low side) and (225-235 high side) vent temp 37-42 out door temp 85-90 degrees.

bohica2xo on Fri July 30, 2010 7:45 PM

Looks like it is a typical conversion.

275psi @ 90f is expected at full heat load. This is what happens when you jump in the truck after soaking in the sun all afternoon & you turn the A/C up to max and drive through the parking lot. No road speed, 1500 rpm & the worst heat load.

The drift in the pressure & cabin temp is the fan clutch modulating.

The doors closed test shows good cooling and reasonable pressures. You should be comfortable driving that truck, and the 225psi should not be an unreasonable strain on the compressor.

B.

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"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.

BG1 on Fri July 30, 2010 8:18 PM

When I closed the windows and the inside temp was at the lowest the compressor would get to a point that it would cycle off and on a few times (about 6 seconds off and 20-50 seconds on) it would do this a few times and then stay on, is this normal?

bohica2xo on Fri July 30, 2010 8:28 PM

Sure is.

When you have 37f vent temps, the evaporator is close to freezing. I would expect to see it cycle at those pressures & temperatures.

How is the cooling at 40 mph? I suspect it cools very well with those performance numbers.

B.

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"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.

BG1 on Fri July 30, 2010 11:34 PM

Maybe I did not need to change to the smaller blue orifice?

Chick on Sat July 31, 2010 6:44 AM

When you changed the condenser, did you make sure you plumed the lines right?? Out of the compressor goes to the top of the condenser, out of the bottom of the condenser goes towards the evap..Some years the lines were the same size and that mistake has been made often...worth a look..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

bohica2xo on Sat July 31, 2010 10:55 AM

I must be missing something here.

You have 37f vent temps on a 90 degree day, on high blower. Low side pressures @ 25psi. Enough cooling to see cycling @ 1500 rpm & high blower. High side pressures below 275 psi.

On a 134a conversion.

What exactly is the complaint?

B.

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"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.

BG1 on Sat July 31, 2010 11:02 AM

No complaint I just commented that possibly the smaller blue orifice was not needed to achieve decent results, Just want to make sure I am not missing anything and that it is within the correct range. Thanks

BG1 on Sun August 01, 2010 11:36 AM

I tried the AC at 40 mph and the temps stayed between 42-44 and the outside temp is at 80. The ac really feels good.

bohica2xo on Sun August 01, 2010 12:26 PM

Well there ya go.

A successful conversion. Usually a pickup will do ok with a 134a conversion, because there is plenty of condensor area, and a small cabin space.

The reason for the blue tube is that 134a can move more heat with the same mass flow of refrigerant. The blue tube reduces the flow into the evaporator so that the heat capacity of the refrigerant more closely matches the original design of the system. Since 134a tends to operate at higher pressures than the R12 did, the smaller orifice also compensates the flow increase from the higher pressures.

The blue tube is part of why your conversion was successful.

B.

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"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.

BG1 on Wed August 11, 2010 7:45 PM

Did the load test on my 1976 Pontiac Firebird that has been changed to R134a. It was changed over to R134a several years ago and leaked down so I added some R134a to get it up and running but its not cooling as well as I would like. At 1500rpm for 5 minutes with the doors open the low pressure stayed close to 30 and the high went up to 360 and the vent temp was at 60 with the outdoor temp at 100-103.
The same test but with doors closed the low was 30 the high was 350 and the vent temp was 54-57.

padgett on Wed August 11, 2010 8:45 PM

re: 76 Firebird

See my comment on the 78 Corvette but have you checked for a bad fan clutch ? Should howl at 2,000 rpm. Poor condenser air flow will push high pressure through the roof without much cooling.

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Many Carpets

TRB on Thu August 12, 2010 12:33 AM

Might help to not confuse posters by starting a new topic when you change vehicles.

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