Engine Size: 2.2
Refrigerant Type: r134a
Ambient Temp: 87
Pressure Low: 45 psi
Pressure High: 170 psi
Country of Origin: United States
I charged up my system the other day and the coolest I could get was 52degrees.I pulled a vacuum of 29.9 and it held a vacuum.I put in 24 ounces of r134a the low side had 45 psi the high side had 170 psi. I put no oil in the system. I next recovered some of the charge and the output temperature of the compressor increase so I think it was not over charged. I made sure that I bled air of the manifold lines before I charged up the system. I pulled a vacuum for 30 minutes.I asking the question if my expansion valve was partially clogged would this cause a higher low side.I am open to you suggestion on this problem.
What engine RPM was this done at? If you were doing this at idle, you may find that the suction pressure comes down to where it ought to be if you bring the engine speed up to 1500-2000 RPM.
52 is pretty good at idle. Should come down at cruising rpm.
I guess this is a conversion job. Charge with R-134a to the full weight specified for R-12 if you can do so and avoid excessive high side pressure. Also the amount of oil is important.
If you've been working on the TXV, make sure the sensor bulb is properly attached to the evaporator outlet line and insulated.
I have a question based on the following comment: "Charge with R-134a to the full weight specified for R-12 if you can do so and avoid excessive high side pressure". I have never heard of charging to the full weight of R-12 at all....is it true that you can do that? What does it mean to "avoid" excessive high side pressure? What would constitute high pressure in that case?
The density of R134a at 72'F is around 90% of that of R12 at 72'F. Therefore, to fill to the same volume of refrigerant you need to add around 90% of the weight of R12.
Excessive high side pressure.... Condenser pressure is directly related to the liquid temperature inside it. Higher the pressure then higher the liquid temperature. If you compare the temperature difference between the condenser liquid and outside air temperature then the bigger the difference the lower the efficiency of the condenser. Typical standard efficiency residential A/C condensers run at 30'F hotter than outside air. The high efficiency condensers run at 20'F difference. This may depend on vehicle/make, but my cars run at a condenser temperature around 40'F hotter than outside air.
If you overcharge your system then, on a TXV system anyways, the excess liquid backs up in the condenser. This gives less remaining vapor area to condense the vapor back to liquid. It essentially makes the condenser look smaller and therefore less efficient. For the condenser to dissipate the heat it therefore has to raise its liquid temperature (and therefore high-side pressure) in order to make a larger temperature difference between it and the outside air in order to dissipate the heat.
Having said the above, if you measure outside air temperature and then measure highside pressure also look on the gauge and pick off the temperature corresponding to that pressure. Subtract the gauge's temperature from the air temperature. If it's much more than 40'F difference then I'd call that excessive high-side pressure. Likely due to too much liquid in the condenser.
Just to add,
the bigger the temperature difference between the condenser's operating liquid temperature (say 120'F or 170psig) and the evaporator's liquid temperature (say 32'F or 28psig) the more refrigerant the system has to pump around to provide the desired cooling. That means more work on the compressor and more heat load on the condenser. This is the second reason (the first in the last post) why R12->R134a retrofitted systems may not cool as well.
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