Car A/C Questions – Sight Glass, Condenser, Hot Outside Temp
June 6, 2012 10:02 am Air Conditioning
Black vehicles never cool as easily as white ones, consider this on your next purchase.
© DenLorsTools.com Summary: ASE Florida Master auto technician answers questions from a reader in Pakistan. Pakistan’s temperatures exceed Florida’s which is normally considered one of the most demanding climates on a car’s AC system. Read on for several questions from Usman in Pakistan.
Usman from Pakistan
OK, I have a few questions.
1- How would I know if my condenser is not clogged up from inside? Its clean and neat from outside though.
2- What’s the purpose of sight glass on the dryer bottle?
3- Why is it that on evenings and mornings, my car ac works perfectly, but in the afternoons, its not so good?
PS I am from Pakistan and here the temperature is around 40-42 C and yeah that is Hella hot
Dennis from Florida
Usman, Wow, I thought we had it hot in Florida! For our readers which are more familiar with Fahrenheit temperature readings, 40-42 Degrees Celsius converts roughly to 104-107 F.
Question – How would I know if my condenser is not clogged up from inside? Its clean and neat from outside though.
Answer – The condenser (located in front of the radiator) can be checked somewhat with an infrared thermometer and looking for extreme temperature differences within a very short span. It is normal to have higher temperatures at he entrance of the condenser and cooler temperatures near the exit and gradual temperature changes in between. Also the gauge readings may indicate a restriction in the condenser if the high side reading is too high and the low side reading is too low. See more on this on our AC gauge readings explained article.
Question – What’s the purpose of sight glass on the dryer bottle?
Answer – The purpose of the sight glass originally was for indicating a low charge of refrigerant. Years ago, I was taught that if there were bubbles passing through the sight glass, the system was low. Do not rely on this 100%. This is just one indicator and I’ve learned long ago from hands on experience that a few bubbles are totally normal. If refrigerant is added until all bubbles are gone the system will surely be over-charged! One good use of the sight glass is to see if there is UV dye in the system without taking anything apart. Also if the system has burnt, contaminated oil in the system, it’s easy to see. The oil and refrigerant passing through the system should either be clear or fluorescent yellow/green and NOT brown or black.
Question – Why is it that on evenings and mornings, my car ac works perfectly, but in the afternoons, it’s not so good?
Answer – The short answer is because there is a decreased demand on the system. It’s important to make sure the system is properly charged and the engine is not overheating. However, in my experience, the best a car’s AC system can be expected to provide is around (3-14 Degrees C) 38 to 58 degrees Fahrenheit “vent air” on maximum cool or recirculate. The difference between the outside and inside temperature can be referred to as temperature drop. This is not to be confused with vent air temperature. This may vary depending on the outside (ambient) temperature and how much radiant heat is being passed through the vehicle. Radiant heat also varies depending upon the color of the vehicle. A black vehicle is very hard to cool because of all the extra heat gained from the heat passed through the exterior into the passenger compartment from the Sun. A white vehicle reflects much of the Sun’s heat in comparison to a dark-colored vehicle. When it’s cooler outside in the mornings and evenings (when the ambient temperature is lower) it makes sense that the AC system will work better even with a fully charged system.
For more information on car air conditioning see the links below.
Related Repair Articles and Products
Paul R. :
Date: July 9, 2012 @ 1:44 pm
Hi. Actually I have a few questions about my car A/C. The High Pressure Switch trips my compressor when the car is IDLE for about 10 minutres, after driving the car for a while on the road. The outside temperature is 122 degrees F. I have replaced the high pressure switch, the condenser, all the relays and fuses to the condenser/ac mag clutch, condenser fan motor, radiator fan motor, flushed radiator. But given the high outside Temperature during mid-day, would this be normal for the high pressure switch to trip my compressor when the car is idle? The compressor trips for 3 minutes, then the compressor runs again, but then after 10 minutes, the high pressure switch trips the compressor again for 3 minutes and this continues to happen. When I am driving, the air is always blowing cold air and the compressor never turns off, except when the interior cabin is cool and it cycles on and off. So after replacing all the components in my car, is this normal?
dennisb - Auto Tool Sales :
Date: July 9, 2012 @ 2:07 pm
Paul, this could be normal because of the extreme ambient temperature. The high pressure switch will in affect turn the compressor off if the high side reading is around 500 psi. This is to protect the compressor. It may be possible to add an extra cooling fan in an attempt to get more air-flow through the condenser. Bottom line is the engineers never planned for that high of temperatures. Good Luck.
Paul R. :
Date: July 9, 2012 @ 3:29 pm
Thanks very much for your response. Very much appreciated. I just wanted to get confirmation as to whether or not it could be something else, e.g. the compressor. I had one final question. My a/c compressor is a Denso rotary vane compressor that takes PAG 150 compressor oil. When servicing the AC, my mechanic added PAG 100 compressor oil instead of PAG 150 compressor oil. Is this a big issue now? Should I flush all the oil out of the compressor/ac system and replace it with PAG 150 oil or is it ok if PAG 100 was added to my AC system that has PAG 150 oil?
dennisb - Auto Tool Sales :
Date: July 9, 2012 @ 3:47 pm
Paul, I personally would not be concerned. The compressor can be drained but not flushed. I think it would be way too much trouble than what it’s worth to try and remove all the oil in the system. Besides not affecting the performance, it won’t void the warranty. Good Luck