Another A/C problem thread!

[KDirk]

Looking for opinions/expertise here. I have noticed on my 88 that when first run after sitting for hours (or over night) that the A/C is cold, and air pressure from the vents is good - maybe not quite great. Now that we are into the interminable STL summer (mid 90's+ daily with humidity pegged at max) I am noticing that the longer I drive the car, the poorer the air pressure is from the vents. I have also noticed that I never seem to have a puddle of condensate on the ground when parking the car after an extended drive with the A/C on.

So, I am speculating that the condensate drain is plugged and causing condensate to backup partially submerging the condenser, thereby blocking the airflow. I had thought that I just had some debris caught on the blower fan side of the condenser, but the way the air pressure at the vents improves again after sitting for some time has me re-thinking that.

So, my next questing is can I safely probe the condensate drain from under the car (going inward) without damaging anything or am I better to remove the blower motor and try to use high pressure air to blow it out? As an aside to this, I have not had any moisture intrusion onto the floor in the cabin. I would have thought a plugged condensate drain would cause it to backup into the car, unless it has someplace else to sneak out.

Hoping to tackle this in the next few days as the A/C cannot keep the car truly comfortable in these temps and I need to restore full flow of air to the vents.

KDirk

[harry yarnell]

I'd pull the blower control module first. You've got a direct eye-shot at the evaporator. As for poking something in the drain bib, you shouldn't hurt anything unless you have something sharp and are forceful. You only need to go in an inch or two.

[Ben Bruce aka First Born]

Kevin, sounds like the evap coil is "freezing". Moisture is freezing on the outside, reducing the air flow. Had a truck once that did this. I was able to turn of the compressor clutch, leaving the blower running.After a few minutes, air flow would come back to normal. I believe the culprit was low freon. An AC shop will probably fix you right up.

Ben

[Machiner 55]

Kevin,

I concur with both Harry and Ben. Won't hurt to probe the drain hole (see pics below) The shiny thing you see in the hole is the bottom of the evap. core.

If you can't see that, then you probably have an obstruction.

John F.

[KDirk]

Thanks for the input. I considered the possibility of low freon causing frost buildup on the evaporator, but when the air comes out full strength, it is plenty cold. Just that the air pressure tapers off after it has been running a while. I will plan on pulling the blower control module today to get a peek at what is going on, and make sure I get the drain unplugged.

FWIW, this car was converted to R134A prior to my ownership, so adding charge will be easy if it's needed.

KDirk

[Guest Mc_Reatta]

Kevin, just to correct the record, you are typing condenser, but are referring to the evaporator.

Yes you may insert a probe up into the drain orifice to clean it out as others have said.

Due to the sensors and programing in the BCM, it would not be possible for the evaporator to freeze up unless you have serious problems (highly unlikely) as the BCM turns the compressor off when the temp of the air leaving the evaporator reaches -2 C or so to prevent this. Also, if the AC charge is low, the BCM will detect that by how quickly the low side temp drops and will trip a warning on the CRT and set a trouble code.

You can verify whats going on by checking the health of the temp sensors, and the low side temperature reading using diagnostics.

My feeling is that you are experiencing early failure symptoms of the blower motor itself. There have been several postings about problems with this fan during short hops around town where the underhood temp changes and problems with air flow coming and going. Replacing the fan motor solved these.

You can see if the fan is being directed to be full on by monitoring BD20 in diagnostics as well. This should rule out the BCM, HVAC module, and Blower Fan Module. Since the flow rate changes dramatically in a short amount of time, it's not likely due to debris on the evaporator face.

[KDirk]

MC,

Thanks! Realized after my last post I had been referring to the evaporator core as the condenser (was typing late last night and just wasn't thinking clearly) but also appreciate your additional input. This looks to be the factory original blower, so I may opt to change it just on account of avoiding sudden catastrophic failure. Had that happen on my Deville, and besides the smell it was awful driving with no air. Of course, it happened on a 95+ degree day.

Haven't been able to do anything today with it as I had another project and now we are getting thunder storms. Maybe it will cool off and I can work under the hood this evening.

KDirk