1999 BMW 740 AC Does Not Cool Well

LOUISSMITH57

MEMBER
1999 BMW 740
V8
2WD
AUTOMATIC
119,532 MILES

My AC works but does not cool very well. On a hot day (95 degrees F) the unit set on MAX takes over 30 minutes to cool the cabin down to a comfortable feel. I have had the freon checked and it is at full capacity. What can be the problem?

Wednesday, June 17th, 2009 AT 1:53 PM

5 Replies

DR LOOT

MECHANIC
2,311 POSTS

It can be a lot of problems;
1. You're outside temperature control sending unit, does her car read the outside temperature correctly?
2. Have you check the condenser to make sure it is clean from dirt and leaves?
3. Can you tell if the A/C compressor is on constantly? Or does it come on and off continuously?
4. You could also be experiencing climate control problems.
5. Also check the air intake vents under the hood make sure they are opening and there is no obstruction in them.
Let me know what you find out.

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Friday, June 19th, 2009 AT 9:27 AM

LOUISSMITH57

MEMBER
5 POSTS

I have checked the air intkae vents and cleaned the filters, also cleaned the filters inside the cabin.

I have noted that the AC fan seems to run at a low speed even on high settings. In the MAX setting for some reason will the fan will jump to a higher speed for a few minutes and then drop down to the normal speed.

I will check the other items that you mentioned.

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Friday, June 19th, 2009 AT 10:46 AM

DR LOOT

MECHANIC
2,311 POSTS

It's starting to sound like it's the climate control unit on in your dash those do go bad but not very often.

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Friday, June 19th, 2009 AT 11:45 AM

LOUISSMITH57

MEMBER
5 POSTS

I got a copy of the BMW 7 Series Manual from Bentley and looked at the AC Troubleshooting guide.

Symptom: AC system does not cool or produces low volume

Probable Cases:
1. AC compressor not engaging
2. Refrigerant charge too low or too high
3. Heater valve malfunction
4. Evaporaor iced up
5. Pressure Switch Faulty

I am pretty sure that 1, 2 and 4 are not the problem, but 3 and 5 could be the problem.

The manual states to test the heater valve and pressure switch, but there are no instructions on "hot to" test these items.

Can you tell me how to the the heater valve and AC pressure switch?

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Tuesday, June 23rd, 2009 AT 12:45 PM

DR LOOT

MECHANIC
2,311 POSTS

Okay we will check three (3) and five (5) the old fashion way'
to check the heater valve, there are three hoses is right behind the engine, checked those and feel if they are hot, if they are, follow the hoses back to the engine until you find the heater control valve you can probably manually turn it off so no hot water is going into the interior of the car, if not use a pair of needle nose vice grips clamp off the main hot hose, and see if it gets any colder inside.
Now to check the AC pressure switch, look at your low side, that is the big hoes until you find a plug-in with two wires, remove the plug and jump the two wires if the A/C compressor kicks on then it's either low on free on or the switch is no good.