This forum topic is a good thread on procedure to measure AC charge on P80 cars from expert jimmy57…
MVS forum user cn90’s opening question:
Since I bought the car new (1998 V70) in 1998, our family has noticed that the AC is “cool”, not ice cold.
- AC Clutch checked/shimmed and gap is 0.30mm. Compressor runs well, zero issues.
- Low Side R134a pressure is 45 psi with engine running and AC “On”.
- Ambient Temp today is 90F.
- Temp at Center Vent (Fan Blower Motor at 3/5 setting) is 68F, or a “temp drop” of only 22F!
- (For comparison purpose, my 1998 BMW 528i has center vent of 60F on the same day, or a “temp drop” of 30F)
- Ideally the “temp drop” (the difference between ambient temp and center vent) should be 30-40F.
So the $1M question for all you guys Volvo heads….how “cold” is your AC?
In other words, what is your “temp drop” when your AC runs properly?
How COLD is your AC? What’s Your Temp Drop?
Looking at Volvo AC Performance in Numbers
jimmy57 » OK, this has to be an apples to apples test. I have a 98. sitting still the other day with engine running 1500 rpm, recirc, windows up, 3/5 fan speed, car was 100+ inside and not in the shade for the test. I had initially 45 psi lo, 265 hi, in 5 minutes it was 32/235 with vent temp in center vent of 57. 5 more minutes 27/230, vent 51. at 15 minutes it would get to 23/225 vent 44 and cycle as it should. Cycling was taking maybe 2 1/2 minutes. I quit then and let it idle. In maybe 3 minutes vent temp was 62 with engine idling and low side was over 40 a bit and high side was 210.
If I go drive the car down the road it does much better. It is noticeably chilly when it is sitting out at 100 ambient with 120 ish inside with rolled up windows. In less than 2 miles of 40 MPH road it is getting really chilly vent temps and getting car cooled down nicely.
Orifice tube/fixed displacement compressor systems are weaker when idling than other systems. Expansion valve can throttle and keep the pressure drop that encourage better evaporator performance when idling with fixed compressor. Varaible compressors are best for little efficiency loss idling.
They do not tell you this on the cans but no one a/c service person who knows what he is doing lets engine idle when A/C is diagnosed. He won’t idle when he is charging if the charging equipment requires system to operate in order for refrigerant to enter (some machines “inject” in increments, others use scale and let system pull in the bulk after initial charge with system off).
A good automotive a/c has a temp drop of 34-37 (with good evaporator airflow, all will cool more if fan is slowed) if you measure inlet temp and vent temp. If you use fresh air and it is 100 then vent will be mid 60’s but only if system is running at design efficiency, i.e., elevated engine speed and electric fan on or engine fan clutch on on engine driven fans. If you go to recirc then the vent temps drop until the interior drops as the inlet air is getting cooler the longer the system runs until the freeze risk point is reached and compressor cycles. Those situations somewhat simulate the car going down the road. The system usually does better moving over 45 mph as airflow is better then then with no fan and just ram effect pushing air over condenser and the air pressure being low under car to help pull the air out of engine compartment.
I’m curious what your car does if you test like I did in the above explanation.
I do believe your Bimmer has an expansion valve a/c system and they have better idle performance. We’ll leave exp valve versus orifice for another day.
https://www.matthewsvolvosite.com/forums/viewtopic.php?p=250368#p250368
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