Automotive Air Conditioning Information Forum

Hi! This my first post and I need help so Thanks in advance!!

I have a 2005 BMW X5 4.8iS. It has 95000 miles and is well maintained. The problem I'm having is my AC does not immediately cool after the car has sat overnight. I live in AZ so instantaneous AC is a must!!

In general what happens is the car is started cold the AC will not blow cold until the engine is to temp and has been revved to over 3500 rpms. Then the air blows great and will continue to blow great for the rest of the day even if its stopped, left to cool off and then restarted.

Here the typical scenario:

Outside temp 82 degF

Gauges hooked up Low 105 psi and High 105 psi

Start cold engine, let run/idle for a few seconds, flip on AC
Compressor is engaged
No change in pressures L 105 psi and High 105 psi
Interior fan running at 1/2 speed, vent temp 90degF
Electric radiator fan not running

Let car continue to run/idle, monitoring pressures, compressor engagement and radiator fan

Engine temp at 1/4 on the dash gauge
Compressor is engaged
No change in pressures
Interior fan running at 1/2 speed, vent temp 90degF
Electric radiator fan not running

Engine temp at 1/2 on the dash gauge (typical running temp)
Compressor is engaged
No change in pressures Low 105 psi and High 105 psi
Interior fan running at 1/2 speed, vent temp 90degF
Electric radiator not running

Quik rev engine to just over 3500 rpm then return to idle
Compressor is engaged
Pressures change Low 40 psi and High 250 psi
Interior fan running at 1/2 speed, vent temp 45degF
Electric radiator running

Engine idles for about 5 min and everything stays constant

Rev and hold engine to just over 2500 rpm
Compressor is engaged
Pressures change Low 30 psi and High 300 psi
Interior fan running at 1/2 speed, vent temp 40degF
Electric radiator running

Return engine to idles for about 5 min and everything stays constant
Compressor is engaged
Pressures change Low 40 psi and High 250 psi
Interior fan running at 1/2 speed, vent temp 45degF
Electric radiator running

If the quik rev to 3500rpms is done the engine temp is greater than 1/4 it typically wont have an effect. Engine temp needs to be at 1/2 position.

So once it kicks in it works great, it's the delay in startup that has me stumped!!

Any help would be greatly appreciated!!

Thanks,
Bill

Bill - if your comfort is OK, then everything is OK.

Cusser - I wish it was that simple but it's my wife's car so everything needs to work without issue.

Al9 - that is most info I've gotten after a year of digging!! Where did you find the displacement control mechanism??

Thanks for the replies!!

Equal pressure on both the low and high sides also suggest to me that the compressor clutch might not be engaging and that you're seeing only static pressures. Are you sure the clutch is energizing, pulling in, and turning the compressor shaft when you turn on the system?

Yes, I've verified the clutch is engaged and the compressor is turning. I also verified when the AC is off the clutch is disengaged.

AI9 - you mentioned that this type of compressor is sensitive to pressure, do my pressures at idle and rpm look ok. I'm wondering if they're a bit high.
Outside temp ~85degF, engine at idle, Low 40 psi and High 250 psi, Interior fan running at 1/2 speed, vent temp 45degF

Engine at 2500 rpm, Low 30 psi and High 300 psi, Interior fan running at 1/2 speed, vent temp 40degF

Thanks!!

brcorp wrote:AI9 - you mentioned that this type of compressor is sensitive to pressure, do my pressures at idle and rpm look ok. I'm wondering if they're a bit high.
Outside temp ~85degF, engine at idle, Low 40 psi and High 250 psi, Interior fan running at 1/2 speed, vent temp 45degF

Engine at 2500 rpm, Low 30 psi and High 300 psi, Interior fan running at 1/2 speed, vent temp 40degF

Those pressures and vent temperatures sound pretty good to me. When your vehicles is moving through traffic you'll also get a ram effect of air through the condenser, and the high pressures will be lower than what you see with just the fan(s) moving the air.

I'm in Arizona too, and my '98 and 2005 Frontiers cool better and faster than my 2005 Yukon (all factory R134) which all do better than my 1988 Mazda truck (R-12). I like your vent temperatures. Next Thursday-Saturday will be 110F or over; but that's measured in the shade !

A few additional thoughts. Are you the original owner of this vehicle, and do you know whether the system has been serviced previously?

Also, Al9 brought up an interesting point about the state of the charge. If you haven't already done so, I suggest having the refrigerant recovered and weighed to determine what's actually in there now. After 15 years, it's probably low if it has never been serviced, possibly resulting in the issues you're experiencing.