How COLD is your AC (what is your "Temp Drop")?

[cn90]

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?

[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.

[rspi]

LOL, I'm not sure what the temp drop is but the yellow sedan I had didn't do to well. Now the wagon I have and the S70 that my daughter drives are both doing very good. If the vent blows on my hands they actually hurt from getting so cold and I have to move the vents off of my arms as well, my arm will ache if I leave the vent on them. My wife makes sure she takes a sweater with her in the car. I'm in Little Rock where it has been breaking records and very few days under 100 degrees F.

To be honest with you, I didn't know that Volvo's AC systems could do this well. I think the system has to be serviced in a balanced way. Good compressor and dryer with the right amount of oil. I did have to shim the compressor in my wagon last fall/summer.

[oragex]

My S60 is also very cold, I need to raise the temperature or it would be too cold inside. I also put a piece of black thick cloth on the dash board to protect it from getting hot from the sun (and also to reduce the dash reflection on the windshield). And I also covered the A/C lines that run inside the engine bay with a few pieces of foam thermal insulation isolation tube pipe.

[abscate]

Old thread alert.

If you set the dash to the right setting for comfort, the car will regulate the temperature right where you like it...

[MrAl]

Hi,

To really compare AC's you have to use the same car as reference unless you know the spec's are the same for both cars. That's because it is not just a matter of measuring the temperature at some point in the system you also have to measure the air flow rate.
If we use a discrete approximation then for example if Car A cools 1 cubic foot of air to 60 degrees F then blows it out in 1 second, and Car B cools 1 cubic foot of air to 60 degrees F then blows it out in 2 seconds, and both cars have the same interior volume, then Car A will cool twice as fast as Car B even thought the measured temperature right out of the vent is 60 F for both cars.

I have the same car, but i never attempted a measurement like this and i think it is a very good idea so i'll do it too. You should state what level your fan was running at, if you can, because mine runs at different levels. Not sure how many levels there are though.
I should be able to do this measurement tomorrow sometime, maybe with different fan level speeds, hopefully.

[abscate]

You can't make these measurements at idle speed btw. The Volvo AC compressor will be working at low capacity and small changes in conditions will give huge changes in results.

Evaluating a Volvo AC has to be done at revs, full on, 15 minutes or more equilibration time.

[MrAl]

Hi there abs,

That's very good information, i'll have to take that into consideration. I hadnt thought about this until yesterday so this is new to me. I also didnt get out there today yet, maybe tomorrow, as it is near 90 so i am avoiding the heat again.

What i would like to do is bring my test equipment out to the car, but unfortunately that means running an extension cord way out there. It would be nice to measure the temperature from before engine start to after engine start, AC turn on, etc., and plot the decrease in temperature over time say every 10 seconds, in several places in the car interior. I think i might be able to do at least one point though, say near one of the vents.
Do you have any idea what the rev should be, like 1500, 2000 rpms or something like that? I wouldnt want to rev it too high for too long though. I think idle is just under 1000 rpms.

[LATER]
I just remembered that my test equipment includes a data logger but i need the PC computer to use that, so i'd have to bring the whole computer out to the car. I dont think this is too easy so i probably wont do that, but maybe it's time to interface to this little Tablet i picked up a couple years back for about 60 bucks. It has no Bluetooth though so i have to come up with a way to interface it to my data acquisition unit (simple PIC chip that reads 4 channel data).

Maybe i'll just sit there and log the temperature with pen and paper every minute with a thermometer

[jimmy57]

The engine speed Volvo mentions is 1500 rpm. I usually see no difference as long as it is at 1200 or a bit more.

[rspi]

Had my '95 serviced before my road trip. About 3 weeks in, a guy had a infared temp gauge so I went for a short spin and checked the vent temp. It was down to 27 degrees F. Outside temp was about 82 F at the time. I was doing 45 mph.