'97 Lumina A/C issue---HELP?

[decollect]

Have replaced compressor and orifice tube and drier. System was vacuumed and proper 134 and oil installed. Now only blows cold when car is in motion. Raising idle does not help. When car comes to halt, 30 seconds later it's blowing slightly cool air (maybe 10 degrees lower than ambient). After car resumes forward motion, 30 seconds later it's blowing cold. Haven't put thermometer in it, but guestimate is when it finally gets as cold as it's gonna gets (after about a minute) it's down to mid to low 50's. Not great but it's a start.
I'm told it is a partially blocked evaporater (under dash). I think it's the condenser (up at radiator) I may have those terms backwards but the locations are accurate. Was told it is the box under dash that's plugged, I'm thinking it is the radiator part up front.
Condenser fan DOES activate when system is turned on. That was my first suspect. Do not know what the pressure readings are.
Is there any way to check at home without gauges to be sure which part is blocked?
When compressor failed, I changed out the compressor, tube and drier at home, then sent car over to local shop for vac and fill. Got car later that day, immediately noticed the problem so took car back. Shop then said that the pressure readings were normal when the tech signed off on job, apparently they didn't road test. Shop pronounced evaporater partially blocked due to slightly high pressure readings. Didn't ascertain which was high, though; low side suction or high side pressure.
HELP? Thanks!!!!

[Blue Bowtie]

You are correct in your terminology. The condenser is mounted in front of the radiator. The evaporator is mounted in the HVAC ducting. If pressures are "normal" as they indicate, and the system cools better once the vehicle is in motion, I'd also suspect a condensing or compressing problem, and not an evaporator. The evaporator does not get significantly more air flow through it once the vehicle is in motion, but the condenser certainly does, and the compressor certainly runs faster, providing more refrigerant flow and potentially a higher differential pressure across the system (better evaporation).

I'd start by inspecting the condenser for contamination such as dirt, insects, plant debris, and road trash. Also look for bent or damaged fins on the tubing which may impede air flow and heat transfer.

You also need to look between the condenser and radiator for obstructions. It is fairly easy to flush through the evaporator and condenser with a garden hose set on a gentle spray in both directions, apply some liquid soap concentrate (even dishwashing soap), and flush it through again to clean the fins as much as possible.

The next thing to check is the efectiveness of the electric cooling fans. Does at least one fan run with the A/C on and engine idling? Are the fan shrouds intact? Are the upper and lower air deflectors (rubber sheet baffles) in place?

Once it's all clean, if the situation persist, try hloding the engine RPMs a little higher while standing still to see if cooling improves.

[decollect]

I'm pretty convinced now it's the condenser. I'm thinking she's plugged. Low side line just off the compressor is just barely cool at idle and vehicle stopped. However running cool water over condenser produces colder airflow into car. Car's pretty clean and both fans are on when A/C is on. All ducting and plastic intact and good, as stated, car's in good shape there. Former police car w/low odometer reading. so it's no wonder the A/C is tired. THAT's the main thing that was running, that and the engine. Car spent alot of it's first 7 years on roadside idling hence low mileage. I'm sure there's enough hours on the engine to equate to about 100k miles, though odo says just 73k now.
Can one run compressed air thru the condenser to check/clear obstructions within? Again, outside of condenser is clean, no blocking debris.
Thanks!

[Blue Bowtie]

If you're thinking that there is an obstruction inside the condenser tubes, it may be better to just replace the condenser. Trying to wash/boil out contaminants could only loosen them, and they might end up in other parts of the system after you close it, like the compressor valves or expansion/orifice tubes. A new condenser is about $140.00

[decollect]

Makes sense. Question. it would seem to me that if I remove the condenser and apply air through it, I should be able to tell if it's restricted based on airflow out of the condenser. yes?
Or are there metering aparati within it that are supposed to restrict flow somewhat. In short, is it like just another radiator inside?
Thanks for all the help.

[Blue Bowtie]

As far as I know, there is no "metering" per se, beyond the arrangement of the distribution tubes and the possibility of turbolators within the tubing to aid heat transfer. Most condensing coils I've dealt with (non-automotive installations) are straight fin tube. The only metering done is at the expansion control and the possible restriction of a filter/drier in the hot gas line. That wouldn't change with vehicle speed.

Any internal restriction in the condenser could be diagnosed with a gauge set. Higher compressor speed would tend to create higher than normal head pressures (high side). A condenser with an internal restriction would likely also have some areas of the coil which are cooler than others, created by the expansion effects of a restriction. You may have to remove the push-pin rivets and pull the grille out of the way for better access to check that.

Air flow is critical. Since you mentioned that raising the idle RPM doesn't make any difference, it's not completely a compressing issue. And at a standing idle, artificially cooling the condenser with water provides increased cooling, which sounds like a condensing issue. Also, while moving and ramming more air through the condenser than a fan possibly could, cooling is improved. I still have a feeling that the condenser is adequately sized and is flowing adequately internally. Still, you can check for cool spots to try to detect any possible internal obstructions, but I would suspect that moving more air is going to be your solution. I wonder if that original electric fan is not losing RPMs (and CFMs) after a lifetime of running on a non-moving vehicle. You might try to compare it to another, similar vehicle if you get a chance. If you get a really good look at the condenser, make sure ALL the fins are straight, and not bent over. There are fin combs available made specifically to repair that condition, and can make a big difference in efficiency.

[decollect]

Pardon the French but Hells Belles, you may have something. If it's restricted internally, moving more air across it wouldn't produce SUCH the difference in cooling. It's still blocked, it's just a tiny bit cooler but blocked and moving more air across it wouldn't allow more Freon to travel into the evaporator quickly enough to produce such a rapid temp change. (under 2 mins from blowing warm at standstill to blowing reasonable cold at 50 mph).
That and I've never really "heard" the fans blowing like you hear some others. Ok, I'll look into that. Makes the best sense I've heard so far.
Thanks a heap, again! -Dave-

[Corndog Man]

I would post your problem on this site. I think these guys are very good at helping with AC problems

http://www.autoacforum.com/categories.cfm?catid=2


Ace

[decollect]

Thanks CD, I'll take ya up on that.

[Supergumby]

What are your system pressures at idle?

Your symptoms sound like an overcharged system.

[MT-2500]

Originally Posted by decollect

Have replaced compressor and orifice tube and drier. System was vacuumed and proper 134 and oil installed. Now only blows cold when car is in motion. Raising idle does not help. When car comes to halt, 30 seconds later it's blowing slightly cool air (maybe 10 degrees lower than ambient). After car resumes forward motion, 30 seconds later it's blowing cold. Haven't put thermometer in it, but guestimate is when it finally gets as cold as it's gonna gets (after about a minute) it's down to mid to low 50's. Not great but it's a start.
I'm told it is a partially blocked evaporater (under dash). I think it's the condenser (up at radiator) I may have those terms backwards but the locations are accurate. Was told it is the box under dash that's plugged, I'm thinking it is the radiator part up front.
Condenser fan DOES activate when system is turned on. That was my first suspect. Do not know what the pressure readings are.
Is there any way to check at home without gauges to be sure which part is blocked?
When compressor failed, I changed out the compressor, tube and drier at home, then sent car over to local shop for vac and fill. Got car later that day, immediately noticed the problem so took car back. Shop then said that the pressure readings were normal when the tech signed off on job, apparently they didn't road test. Shop pronounced evaporater partially blocked due to slightly high pressure readings. Didn't ascertain which was high, though; low side suction or high side pressure.
HELP? Thanks!!!!

As said we need the pressure readings.
Check low and high pressure at adle and at 2000 RPM with compresser running and fan running and blowing threw rad and condenser and post back readings.
MT