Quote:
Originally Posted by Tech II
Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees...
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I've come to trust your opinions on most everything; so hearing that from you makes me question my sanity. I quit working on A/C professionally two decades ago. A/C systems must have really taken a performance dump since then...or I just happen to live in a place where I never had to deal with crazy high ambient temperatures.
Thousands of years ago, dinosaurs ruled the earth. A/C systems were controlled with a POA/STV; and they could be adjusted to provide 33 degree evaporator temperature--just above where the evaporator freezes.
In an effort to cut costs--(deceiving the public by pretending to make the system more "fuel efficient")--GM went to a cycling compressor clutch system. The moderately-expensive, precision-made POA/STV was replaced with a thirty-cent plastic screen that had a metal orifice molded into it, and an O-ring to seal it inside the refrigeration pipe. The duct temperatures were now in the 40--45 degree range, instead of 35 degrees. The only fuel economy gains were from a mechanically more efficient compressor, and the REDUCED COOLING provided by the new system.
If an A/C system can't provide 45 degree duct temperature, there's something wrong.
60 degrees is crazy. I absolutely guarantee you that if I had 90+ degree duct temps because it was hotternhell outside, and the A/C system I just worked on only reduced the temp by 30 degrees...customers would have had my ass on a flagpole.
Ambient temps vary, duct temp was fairly stable. The high-side pressure went up as ambient temp increased; and you can kiss "goodbye" to any clutch cycling--that "fuel efficient cycling clutch" compressor ran
constantly just like with the old STV systems.
I'm trying to understand how we can be so far apart on this. There must be something I'm not understanding.
Quote:
Originally Posted by Tech II
I think we have a capacity problem here......really unknown how much refrigerent is in the system, since we have guys adding 1/2 cans...only accurate way to add freon is recover and evac the system, then add freon by weight......
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I understand that young guys would believe this. It's what you've been trained to do; and it gets the charge very close without wasting refrigerant OR a lot of time thinking. Also eliminates arguing with the customer because the shop can point to the "factory specs"; as long as they added the "correct" amount, they figure they're off-the-hook for performance issues. So, sure, it's a successful and politically-correct way to service the unit. (Most of the time.)
'Course, it assumes that you've got access to the multi-thousand dollar recovery unit/recharge station.
It also assumes that there's no aftermarket refrigeration-system changes, such as a replacement hose that has a muffler that the OEM hose didn't; or an extra-large condenser in place of a regular-size condenser because the correct size condenser is discontinued. Recharging based on adding a specified weight of refrigerant is inaccurate as soon as the capacity of the system changes from OEM spec. Truth is, adding by specified weight is a great way to be close, but not exact in the best of circumstances.
In the old days, the mechanic would top off refrigerant slowly until the MAXIMUM COOLING was achieved--add some, watch the thermometer in the duct. Add some more, check the thermometer. When the thermometer JUST starts to go UP--maybe a degree or two--you've there. That procedure works on ANY vehicle, even if the cooling system doesn't meet OEM specs for capacity.