AC help on 72 coupe
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,518
Likes: 37
From: The Woodlands Texas
AC help on 72 coupe
So I've got a problem, or so I think.
On my 72 sb coupe that was restored 5 yrs ago, I'm having problems with my AC. I just bought the car and it was in NC and hadn't been run much since the restoration. Here is what has transpired.
1) When I first got it, the compressor would kick in and out like it was low on R132 (yes, it's converted). Sure enough it took 3 cans.
2) After filling, it was better but it would still kick in and out. We identified that there was a connector that wasn't making contact correctly and that was fixed.
3) AC started working, but not very well. We did a complete vaccum leak test and found nothing.
4) Diagnosed that the condensors were over heating and this caused the R132 to be discharged as it built pressure.
5) Root cause was that the fan shroud was missing the bottom section of the two piece shroud. This was an obvious oversight during the restoration, but in the mountains of NC it didn't matter. What this casused was a lack of vaccum from the fan to pull enough air through the condensors keeping them cool.
6) Shroud is now correct and there is significant air flow change. The AC unit is working......BUT, the compressor seems to be surging. The unit is cooling the air fine, but when I drive and the compressor is engaged, I feel a inconsistant drain/pull on the engine. Inconsistant meaning it changes.....it will seem to be running fine and then all of the sudden I can feel the engine bog down more than normal for a few seconds ( at normal engine speeds...45 mph) and then return to normal AC bogging. It surges back and forth but the compressor never seems to kick out like it did before.
Is this normal? The air is cold, but not ice cold. It seems to be working though. I'm guessing since the engine is only 200 HP, this is normal. I'm just not sure though.
Thoughts?
On my 72 sb coupe that was restored 5 yrs ago, I'm having problems with my AC. I just bought the car and it was in NC and hadn't been run much since the restoration. Here is what has transpired.
1) When I first got it, the compressor would kick in and out like it was low on R132 (yes, it's converted). Sure enough it took 3 cans.
2) After filling, it was better but it would still kick in and out. We identified that there was a connector that wasn't making contact correctly and that was fixed.
3) AC started working, but not very well. We did a complete vaccum leak test and found nothing.
4) Diagnosed that the condensors were over heating and this caused the R132 to be discharged as it built pressure.
5) Root cause was that the fan shroud was missing the bottom section of the two piece shroud. This was an obvious oversight during the restoration, but in the mountains of NC it didn't matter. What this casused was a lack of vaccum from the fan to pull enough air through the condensors keeping them cool.
6) Shroud is now correct and there is significant air flow change. The AC unit is working......BUT, the compressor seems to be surging. The unit is cooling the air fine, but when I drive and the compressor is engaged, I feel a inconsistant drain/pull on the engine. Inconsistant meaning it changes.....it will seem to be running fine and then all of the sudden I can feel the engine bog down more than normal for a few seconds ( at normal engine speeds...45 mph) and then return to normal AC bogging. It surges back and forth but the compressor never seems to kick out like it did before.
Is this normal? The air is cold, but not ice cold. It seems to be working though. I'm guessing since the engine is only 200 HP, this is normal. I'm just not sure though.
Thoughts?
Last edited by CWerner; May 17, 2012 at 11:03 PM.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
So I've got a problem, or so I think.
On my 72 sb coupe that was restored 5 yrs ago, I'm having problems with my AC. I just bought the car and it was in NC and hadn't been run much since the restoration. Here is what has transpired.
1) When I first got it, the compressor would kick in and out like it was low on R132 (yes, it's converted). Sure enough it took 3 cans.
2) After filling, it was better but it would still kick in and out. We identified that there was a connector that wasn't making contact correctly and that was fixed.
3) AC started working, but not very well. We did a complete vaccum leak test and found nothing.
4) Diagnosed that the condensors were over heating and this caused the R132 to be discharged as it built pressure.
5) Root cause was that the fan shroud was missing the bottom section of the two piece shroud. This was an obvious oversight during the restoration, but in the mountains of NC it didn't matter. What this casused was a lack of vaccum from the fan to pull enough air through the condensors keeping them cool.
6) Shroud is now correct and there is significant air flow change. The AC unit is working......BUT, the compressor seems to be surging. The unit is cooling the air fine, but when I drive and the compressor is engaged, I feel a inconsistant drain/pull on the engine. Inconsistant meaning it changes.....it will seem to be running fine and then all of the sudden I can feel the engine bog down more than normal for a few seconds ( at normal engine speeds...45 mph) and then return to normal AC bogging. It surges back and forth but the compressor never seems to kick out like it did before.
Is this normal? The air is cold, but not ice cold. It seems to be working though. I'm guessing since the engine is only 200 HP, this is normal. I'm just not sure though.
Thoughts?
On my 72 sb coupe that was restored 5 yrs ago, I'm having problems with my AC. I just bought the car and it was in NC and hadn't been run much since the restoration. Here is what has transpired.
1) When I first got it, the compressor would kick in and out like it was low on R132 (yes, it's converted). Sure enough it took 3 cans.
2) After filling, it was better but it would still kick in and out. We identified that there was a connector that wasn't making contact correctly and that was fixed.
3) AC started working, but not very well. We did a complete vaccum leak test and found nothing.
4) Diagnosed that the condensors were over heating and this caused the R132 to be discharged as it built pressure.
5) Root cause was that the fan shroud was missing the bottom section of the two piece shroud. This was an obvious oversight during the restoration, but in the mountains of NC it didn't matter. What this casused was a lack of vaccum from the fan to pull enough air through the condensors keeping them cool.
6) Shroud is now correct and there is significant air flow change. The AC unit is working......BUT, the compressor seems to be surging. The unit is cooling the air fine, but when I drive and the compressor is engaged, I feel a inconsistant drain/pull on the engine. Inconsistant meaning it changes.....it will seem to be running fine and then all of the sudden I can feel the engine bog down more than normal for a few seconds ( at normal engine speeds...45 mph) and then return to normal AC bogging. It surges back and forth but the compressor never seems to kick out like it did before.
Is this normal? The air is cold, but not ice cold. It seems to be working though. I'm guessing since the engine is only 200 HP, this is normal. I'm just not sure though.
Thoughts?
You say you did a complete vacuum leak test and found no problems. Are you saying you emptied the system of refrigerant, vacuumed it out with a pump, and then shut the pump down and closed the gauges for a period of time to see if vacuum was held? If you aren't sure the system is properly sealed, the refrigerant could have leaked out in short order. If so, lack of refrigerant could cause the compressor to cycle.
Lastly, is the work being performed by a qualified person?
Thread Starter
Drifting
Joined: Jan 2008
Posts: 1,518
Likes: 37
From: The Woodlands Texas
Jud,
The vacuum leak test was done just as you say, by a qualified auto service shop with all of the proper tools and equipment. They believe that there is no leak in my system. When I described the R132 discharging, it was through the relief valve not through a leak.
So the question remains.... Is the surging I'm describing normal or an abnormal condition?
The vacuum leak test was done just as you say, by a qualified auto service shop with all of the proper tools and equipment. They believe that there is no leak in my system. When I described the R132 discharging, it was through the relief valve not through a leak.
So the question remains.... Is the surging I'm describing normal or an abnormal condition?
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Hard to say on the compressor surging, as the system's been converted to 134a, and the condensor may be a bit on the smallish side. As for possible leaks, the compressor shaft seal relies on internal system oil for lubrication, and may leak when dries up sitting awhile. Might be fine now since runing it, circulating the oil. Good idea giving the system an internal UV trace dye shot, and occasionally scanning around with a UV light, to keep an eye on things.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Jud,
The vacuum leak test was done just as you say, by a qualified auto service shop with all of the proper tools and equipment. They believe that there is no leak in my system. When I described the R132 discharging, it was through the relief valve not through a leak.
So the question remains.... Is the surging I'm describing normal or an abnormal condition?
The vacuum leak test was done just as you say, by a qualified auto service shop with all of the proper tools and equipment. They believe that there is no leak in my system. When I described the R132 discharging, it was through the relief valve not through a leak.
So the question remains.... Is the surging I'm describing normal or an abnormal condition?
One thing I can tell you that might help the cooling is to look at the weather strip on the rear of the hood which seals the engine compartment's hot air, keeping it from entering the cowling and duct work. If it's not in excellent condition, or missing, replace it. It's very cheap and an easy job to do.
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
your 70 doesnt use any type of clutch cycling system. Once its engaged it should stay engaged,
Is your fan clutch operating correctly? Are you using a POA valve redesigned for the R134?
You could be drawing liquid refrigerant back into the compressor causeing a potentially damaging liquid lock condition
Is your fan clutch operating correctly? Are you using a POA valve redesigned for the R134?
You could be drawing liquid refrigerant back into the compressor causeing a potentially damaging liquid lock condition
