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Low side seems low

numbo on Sun June 27, 2010 8:37 PM User is offline

Year: 1989
Make: chrysler
Model: TC Maserati
Engine Size: 2.2
Refrigerant Type: 134A
Ambient Temp: 85
Pressure Low: 15
Pressure High: 215
Country of Origin: United States

At 1700 to 1800 RPM the low side is at 15 and high is at 215 without any on or off cycling. When running at idle (about 700 RPM) low is 25 and high at 185 also no cycling. Outside air temp
is about 85. I had a fan blowing into the condenser. The vent temps were good about 45 to 48. I'm happy with the vent temps but the low side seems low and I'm worried that
when it gets cold outside (winter time) and I need the defroster that the low side might bottom out.
I thought I would check this out and see if anyone has any thoughts on why the low side is so low and yet I get good vent temps. At 85deg. X 2.3 is 195.5 so I am only about 10lb off on the high side.
Thanks for any info..........
Don

Briandl79 on Sun June 27, 2010 9:09 PM User is offline

Why did you have a fan blowing into the condenser?

bohica2xo on Sun June 27, 2010 9:43 PM User is offline

Some TXV systems run seemingly low pressures. Check the suction line at or near the evaporator - is it icing over or just cool?

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.

numbo on Sun June 27, 2010 10:33 PM User is offline

To simulate more of a driving condition.

numbo on Sun June 27, 2010 10:35 PM User is offline

The TXV is cool on the return line.

Briandl79 on Sun June 27, 2010 11:09 PM User is offline

Quote
Originally posted by: numbo
To simulate more of a driving condition.

Not sure that's necessary, or even a great idea.

mk378 on Sun June 27, 2010 11:25 PM User is offline

How much R-134a is in the system? Should be close to the R-12 specified amount. It is common to undercharge conversion jobs trying to keep the high side down. You could try to run more charge and let the high side rise some. TXV systems cycle on evaporator temperature and you're not quite there yet. At 15 psi low side, (1800 rpm test) the evaporator should be colder than it is.

bohica2xo on Mon June 28, 2010 1:34 AM User is offline

Worry more about returning oil to the compressor than the low temperature performance.

Mk378 is right, if the suction is only cool @ 15psi you are undercharged. Conversions run higher pressures than we really want sometimes. 2.3 as a factor? I wish. 2.7 is good, and some run up around 3.25...

A full load test should simulate a worst case. Doors open, cabin fan on highest speed. 1500+ engine rpm. Hold that condition for five minutes, then record pressures while engine is still above 1500 rpm. No fan in front of the condensor, unless the car is equipped with one all the time.

A high side under those conditions of 275 to 290 would not be unexpected @ 85 to 90f ambient.

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.

numbo on Mon June 28, 2010 8:24 AM User is offline

Thanks everyone for your help. I'll tweak it a bit more.
Don

Edited: Mon June 28, 2010 at 8:26 AM by numbo

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