A/C Help

[mLuMaN83]

So heres the deal. When I get in the car, the AC blows great. Ice cold. But then after say 20 min or so, it decides to go luke warm. Also if I change to face and defroster, I feel cold air through the face vents for a second then goes luke warm again and blows hot air out the defroster. If I turn the car off for awhile and get back in, the AC works fine again and then after a bit, goes luke warm. I brought the car in last year for an evac and recharge and they said it was full and pressure was good and that they think the issue may be in the AC control unit itself.

Do I actually need an evac and recharge? Or could it be the control unit?

[kayger12]

See if the air on the drivers side is colder than the air on the passenger side when you're putting it through the dash vents.

[mLuMaN83]

It is slightly cooler on the drivers side then the passenger side. The odd thing here is that if the car sits awhile or overnight, and I jump in and go, the air is ice cold for about 20 min then all the sudden, it goes warm.

[kayger12]

I've read before that temperature differential between the two sides is a sign of low refrigerant.

I'd start there and then move on to trouble shooting the compressor.

Can the FSR affect that or is it only the blower speed?

[mLuMaN83]

Blower is fine. It's almost like the control unit is telling the flaps to do the wrong thing because if I change the vent, i feel ice cold for a second come out the face vents. I and thinking of buying a cheap used control unit off ebay and see what happens. If that doesnt work, then maybe go for an evac and recharge.

Weird weird. Either way, it's gotta get fixed. I live in Florida.

[LivesNearCostco]

Set your OBC to display exterior temp, see if it's roughly accurate. If it displays a much lower exterior temp than outside, it could shut off the A/C because it thinks it's cold outside. Or maybe your heater valve is broken?

[echo46]

I agree with KG, sounds like low refrigerant. You can hook up an AC guage and check the pressure to see if it needs a boost. You aRe checking the vacuum and pressure psi of the system. The high and low pressure can diagnose a lot of problems. Fairly easy. If you are doing it yourself, don't allow any to escape as it is fairly toxic and there are strict environmental laws concerning its capture. If you suspect a leak, which I don't here, you can put a tracer dye in the system serif it appears at any of the connections or the compressor. I replaced most of the AC system on my E36. Not that difficult.

[telijah]

It is not indicative of low refrigerant. Low refrigerant would not have cool air one moment then warm the next over and over. It is likely what LiveNearCosco said. There is also a water valve under the hood that I believe I've heard cause similar symptoms, #2 here.

To answer Kayger's question about the FSR, the FSR only shows symptoms of erratic or no blower control.

[echo46]

Couldn't the compressor be going bad also?

[WOLFN8TR]

You also need to get a pocket thermometer to check the temp coming out of the vents. A Low charge will make the compressor cycle on/off. My AC blows approx 35-38 degrees on Max. Good luck!