Air conditioner problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

s95930 · 07-02-2005, 10:45 PM

I finally replaced the clutch on my AC. It is cooling well. Works fine at idle and around town but when i get out on the highway between 55-65 it freezes up.

Any Ideas?

JimKshortstep4x4 · 07-03-2005, 06:25 AM

Does the ac continue to work when the ice forms on the outside of the pipes?

Jim

355 · 07-03-2005, 07:59 AM

Do you have condensor coil cooling fans. Do you have a seperate relay to turn on your fans or is it common with your compressor clutch relay. I had the same problem with an old air system. The fan motors are permenant magnet motors, at highway speeds the blades are driven by the wind and the motor becomes a generator. It produced enough power to hold the clutch in and freeze everything up. I added another relay to isolate the fans from the clutch and have had no problems since. Don't ask how long it took to figure this one out. Steve

s95930 · 07-03-2005, 08:47 AM

Quote:

Originally Posted by JimKshortstep4x4

Does the ac continue to work when the ice forms on the outside of the pipes?

Jim

No it slowly looses air flow. I have to tun off the AC and let thaw out.

s95930 · 07-03-2005, 08:49 AM

Quote:

Originally Posted by 355

Do you have condensor coil cooling fans. Do you have a seperate relay to turn on your fans or is it common with your compressor clutch relay. I had the same problem with an old air system. The fan motors are permenant magnet motors, at highway speeds the blades are driven by the wind and the motor becomes a generator. It produced enough power to hold the clutch in and freeze everything up. I added another relay to isolate the fans from the clutch and have had no problems since. Don't ask how long it took to figure this one out. Steve

I have electic fans on my truck. But I don't think it has anything to do with my problem. When the AC is on the cluch on my system does not cycle on and off.

Zeke · 07-04-2005, 05:36 AM

Could be a low on refrigerent this will cause the evaporator to freeze up. Might try adding a small amount at a time to see if it helps.

68C15 · 07-04-2005, 07:37 AM

I could be wrong but it sounds like a POA valve problem.

chickenwing · 07-06-2005, 11:28 AM

Clutch on our trucks is engaged continuosly when a/c is selected. Evaporator freeze-up in a properly functioning system is prevented by the poa (pilot operated absolute) valve.

I am too new to A/C to arm chair diagnose your problem. You can try asking over in the a/csource forum. Be prepared to provide high/low gauge readings though.

Putter · 07-06-2005, 11:57 AM

I agree with zeke. Check for low refrigerent. That has happened to me before.

**Richard** · 07-07-2005, 01:08 AM

Freezing can be caused by an overcharge condition, not an undercharge. Low airflow at the evaporator or condenser can also cause freezing. Seeing as you probably have plenty of airflow across the condenser at highway speeds- that is out. Leaves and other crud coming in through the cowl can clog the evap coil. A sticking POA valve is another definite possibility. Check the airflow in the cab at all fan speeds. if it is fine probably the POA.

Don Smith · 07-07-2005, 10:17 AM

I had same problem, replaced expansion valve and it did not cure problem. Tried to find new POA valve but they are not avail. Repaced POA valve with an adjustable valve that cycles the compressor off before evap. freeze up. Works fine now.

grebus1 · 07-07-2005, 12:43 PM

Just to be clear (I am an AC novice), the compressor does not cycle on and off if the truck has a factory set-up? If that is so, isn't that unusual compared to the way most vehicles' AC behaves?

Gene · 07-07-2005, 02:04 PM

You ar correct, as I am an A/C novice myself, I asked this same question when I was getting ready to recharge my system after re-installing a new compressor. My system was bone dry and I turned on the A/C and the compressor stayed engaged. This as I was told is normal function for these model year trucks. There is a single switch that supplies power to the compressor clutch and when this switch is made the compressor stays on always.

chickenwing · 07-07-2005, 02:30 PM

You can get a poa eleminator kit that will turn your system to a cycling clutch. Old air products. Around $100.

07-02-2005, 10:45 PM	#1
s95930 A-Adam A-Adam Join Date: Apr 2003 Location: Sarpy Co. Ne. South of Omaha Posts: 263	Air conditioner problem I finally replaced the clutch on my AC. It is cooling well. Works fine at idle and around town but when i get out on the highway between 55-65 it freezes up. Any Ideas? __________________ 70 3/4 ton GMC Camper Special Last edited by s95930; 07-02-2005 at 10:46 PM.

07-03-2005, 07:59 AM	#3
355 Registered User Join Date: May 2005 Location: South Mississippi Posts: 81	Do you have condensor coil cooling fans. Do you have a seperate relay to turn on your fans or is it common with your compressor clutch relay. I had the same problem with an old air system. The fan motors are permenant magnet motors, at highway speeds the blades are driven by the wind and the motor becomes a generator. It produced enough power to hold the clutch in and freeze everything up. I added another relay to isolate the fans from the clutch and have had no problems since. Don't ask how long it took to figure this one out. Steve __________________ 1969 C10 Long Step,355,700r4w/lockup, HEI,Weiand,750 Performer,1.6 rockers,Camel Humps,Comp 262Extreme,Hedman,2 1/2"pipes, tele/tilt,SunRoof,ps,Disc pb,ac,Cragar,eaton,Corvette style roll pan, Bowtie louvered tail gate,lowered 2/2.

07-04-2005, 05:36 AM	#6
Zeke Active Member Join Date: Jun 2002 Location: L.A. Lower Alabama Posts: 453	Could be a low on refrigerent this will cause the evaporator to freeze up. Might try adding a small amount at a time to see if it helps. __________________ 1969 C10 350 3spd 1995 GMC 3500 XC 350 dually When Thomas Edison worked late into the night on the electric light, he had to do it by gas lamp or candle. I'm sure it made the work seem that much more urgent. George Carlin

07-04-2005, 07:37 AM	#7
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	I could be wrong but it sounds like a POA valve problem. __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

07-06-2005, 11:28 AM	#8
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	Clutch on our trucks is engaged continuosly when a/c is selected. Evaporator freeze-up in a properly functioning system is prevented by the poa (pilot operated absolute) valve. I am too new to A/C to arm chair diagnose your problem. You can try asking over in the a/csource forum. Be prepared to provide high/low gauge readings though. __________________ The truck... you hear that? No really, you did hear that?!!!

07-03-2005, 06:25 AM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Does the ac continue to work when the ice forms on the outside of the pipes? Jim

07-06-2005, 11:57 AM	#9
Putter More Cowbell.... Join Date: Mar 2004 Location: Puckett, MS Posts: 3,569	I agree with zeke. Check for low refrigerent. That has happened to me before. __________________ *There once was a member from Puckett.....Who ( fill in the blank blank blank* ) bucket**

07-07-2005, 01:08 AM	#10
Richard Senior Member Join Date: Dec 1999 Location: Southern California Posts: 2,810	Freezing can be caused by an overcharge condition, not an undercharge. Low airflow at the evaporator or condenser can also cause freezing. Seeing as you probably have plenty of airflow across the condenser at highway speeds- that is out. Leaves and other crud coming in through the cowl can clog the evap coil. A sticking POA valve is another definite possibility. Check the airflow in the cab at all fan speeds. if it is fine probably the POA. __________________ Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746

07-07-2005, 10:17 AM	#11
Don Smith Registered User Join Date: Jul 2000 Location: Hampton, Ga, USA Posts: 217	I had same problem, replaced expansion valve and it did not cure problem. Tried to find new POA valve but they are not avail. Repaced POA valve with an adjustable valve that cycles the compressor off before evap. freeze up. Works fine now. __________________ 68 Short Stepside, 350, quadrajet, 700r4, 3:73 posi, power front discs, HEI, Factory Air, Tilt, Tach, accelerator cable instead of rod, sway bar. 96 Impala SS 97 Monte Carlo

07-07-2005, 12:43 PM	#12
grebus1 Registered User Join Date: Feb 2000 Location: Edmonds, WA Posts: 322	Just to be clear (I am an AC novice), the compressor does not cycle on and off if the truck has a factory set-up? If that is so, isn't that unusual compared to the way most vehicles' AC behaves? __________________ '72 Chevy Suburban Custom Deluxe 10, 402/TH400

07-07-2005, 02:04 PM	#13
Gene Registered User Join Date: Aug 2002 Location: Muskogee, Oklahoma Posts: 2,914	You ar correct, as I am an A/C novice myself, I asked this same question when I was getting ready to recharge my system after re-installing a new compressor. My system was bone dry and I turned on the A/C and the compressor stayed engaged. This as I was told is normal function for these model year trucks. There is a single switch that supplies power to the compressor clutch and when this switch is made the compressor stays on always. __________________ 1971 SWB 4X4 Build BOARD MEMBER #5448 BOOMER SOONER!!!!

07-07-2005, 02:30 PM	#14
chickenwing Lovin' Life in Miss.! Join Date: Mar 2004 Location: Puckett, Mississippi Posts: 1,937	You can get a poa eleminator kit that will turn your system to a cycling clutch. Old air products. Around $100. __________________ The truck... you hear that? No really, you did hear that?!!!



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