new engine now air conditioner/defrost issue

I just had a remanufactured engine put in my 92 Astro van 4.3 with W in the vin. The engine runs great, and I picked it up yesterday, and was totally satisfied. It was 74 degrees here in Virginia yesterday, so I didn't use any climate control . I woke up today to go to work, and it's in the 30's, so I let the van warm up, and put on the defroster as I backed out of the driveway. Right away something under the hood(sounding something like a fan hitting a shroud) starts making noise. I start going through my control setting on the dash to see how they function, and I notice there is no such sound when I'm using the heater. So I tested the AC, and there is no cold air coming out of it. The heater, and defrost are blowing warm air just fine. Also, it feels like there is a cycled drag on the motor, almost like something hooked to be back of the van, and it happens in revolution type cycles, just for a split second. I take it right back to the repair shop, and the guy drives it and says he feels nothing, and that it is a sound in my dash area. I found out from him that the defrost also works with the air compressor just like the AC, so it seems to have something to do with the compressor. I can put my hand in front of the interior vents when the AC is on, and the air is barely cold, much like when you have a car that the AC isn't cooling any more. He said he had to discharge the compressor, and then recharge it during the engine replacement, but he feels like if anything is wrong with the defrost/AC that it has nothing to do with the engine replacement. I left it with him all day, and he called me to tell me it's ready, and I asked him if it was fixed, and he said they added some oil, and tightened a few brackets, but I still get the feeling that he's playing dumb, and won't acknowledge a problem to start with. He said "I need to make the determination if it's alright when I pick it up in the morning". I'm sorry for the long post, but does anyone have any ideas what it might be? I'm not imagining it as he seems to act like I am. Also, he put a meat therm. in the int. vent while the AC was on and it went down to below 40 degrees but when I put my hand up to the vent, it is not blowing cold air like it did before, I don't care what the therm says. My uneducated guess is that something is up with the compressor, and he's acting like I'm just imagining it all. This is a reptutable place, and I just dropped $2911.48 there for the engine replacement, and I can't afford to have AC work done when all was well before. Thank you all very much for any help you can give me. John Sr.

Hi- I have a '94 Astro- Just replaced the engine in it myself- bought a used 117K mile engine for $500- mine had had 315,000 when the rod bearings starting knocking- Glad to know I saved $2400- any way- I also do A/C work on all GM products- what you are hearing is the compressor coming on and off (cycling) due to low load conditions- if it is 30 degrees out- don't expect the a/c to cool very much- the compressor may or may not come on any way at such low temps- To adequately test it- you need to have it in at least a 70 degree environment- and then look for vent temps of around 38- 40 deg f on lower blower speeds- the fan may be rubbing the shroud at different points- a simple adjustment is needed if this is the case. Does the air come out of the vents as requested- most times a vacuum leak will cause the air to always come out the defrost- no other places- if the air comes out where it should and the compressor is turning on and off at low load- 30-40 degrees ambient- you probably don't have a problem. Have the mechanic check the fan shroud- for rubbing and go from there....

Hi- I have a '94 Astro- Just replaced the engine in it myself- bought a used 117K mile engine for $500- mine had had 315,000 when the rod bearings starting knocking- Glad to know I saved $2400- any way- I also do A/C work on all GM products- what you are hearing is the compressor coming on and off (cycling) due to low load conditions- if it is 30 degrees out- don't expect the a/c to cool very much- the compressor may or may not come on any way at such low temps- To adequately test it- you need to have it in at least a 70 degree environment- and then look for vent temps of around 38- 40 deg f on lower blower speeds- the fan may be rubbing the shroud at different points- a simple adjustment is needed if this is the case. Does the air come out of the vents as requested- most times a vacuum leak will cause the air to always come out the defrost- no other places- if the air comes out where it should and the compressor is turning on and off at low load- 30-40 degrees ambient- you probably don't have a problem. Have the mechanic check the fan shroud- for rubbing and go from there....
Thanks brcidd,
I picked it up today, and all is well. As far as the compressor coming on and off; I know that's what it was, but the sound was way to loud inside the van, and it never had that sound before. Anyway; it seems to be fine now, and even though it was a pretty penny; I'm extremely happy with the job. I was sitting at a stop light today, and I coulding even feel or hear the engine running, and this is no exaggeration either. My previous engine had 228,000 on it, and it was still strong as can be. I was in passing gear while passing a wrecker that was throwing big chunks of broken glass at my windshield from a car it was towing, and I got caught with to little time to pass with a car approaching from the other direction, ans I had to floor it while already in passing gear, and it spun a rod bearing. Even after the bearing spun; the engine was running like a top; except the rod knocking of course. This Astro van has been the best van I've ever owne, and I've owned about 5 different models. Thanks again for the quick answer. John Sr.