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72 Cutlass A/C help needed

mikecap67 on Mon July 12, 2010 4:24 PM User is offlineView users profile

Year: 1972
Make: Olds
Model: Cutlass
Engine Size: 455
Refrigerant Type: R-12
Ambient Temp: 89
Pressure Low: 28.5
Pressure High: 135
Country of Origin: United States

At idle (800 rpm) sitting in the drive way fans running (dual electric pullers), engine temp 160, low side 28.5/high side 135, recirc on, fan speed low, duct temp 43f, rear 1/2 POA valve frosts over, rear compressor low side frosts over
At idle (800 rpm) sitting in the drive way fans running (dual electric pullers), engine temp 160, low side 28.5/high side 135, recirc on, fan speed max, duct temp 53f, rear 1/2 POA valve frosts over, rear compressor low side frosts over

Engine speed 1800 rpm, sitting in the drive way fans running (dual electric pullers), engine temp 160, low side 28.5/high side 140-142 (low side drops to 24.5 when revving, and then recovers to 28.5), fan low, duct temp 62, poa sweats

Driving the car (2200 rpm) 35 mile interstate drive, engine temp 160: A/C on recirc, Fan on max duct temp is 72, on med/high its 68, med its 62, low its 56. Duct temp will drop 5-7 degrees when I get off the interstate and pull up to stop sign, then climb 10-12 when I pull away. Pop the hood and the POA valve is ICED over and the rear compressor low side fitting is ICED over. No ice anywhere else.

After car is warm and A/C has been running for awhile, if I sit at idle the duct temp will get to the mid 60's, but as soon as I pull away it will sometime climb to 80 degrees or so before slowly working back down.

Thanks for the help!



-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

mk378 on Mon July 12, 2010 5:00 PM User is offline

Frost / ice on the POA should mean you're getting good refrigeration performance (maybe too good, evaporator icing?). If there is air in the refrigerant system the evaporator can ice even though the POA is maintaining proper evaporator pressure.

Perhaps it's a reheating problem. Tried clamping off the heater hoses? Also are the air doors vacuum operated? There is maximum vacuum idling it is less when driving.

mikecap67 on Tue July 13, 2010 1:26 AM User is offlineView users profile

Heater control valve is working and so are the doors (closes for recirc). The car does not have the superheat option.

-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

jglanham on Tue July 13, 2010 12:47 PM User is offline

You stated that the heater control valve and blend doors are working. What you didn’t say was if you tried clamping the heater hoses and if the blend doors are vacuum operated. Your vehicle is 38 years old. If you haven’t replaced the heater valve recently, it could be leaking even though the actuator shows it closed. Clamp the hoses to make sure. If the blend doors are vacuum operated, they could also be leaking. They are a metal canister with a diaphragm that has a metal actuator attached. You indicated that as soon as you pull away, the temp climbs, then settles back after a while. Consider this: Pinhole leak in diaphragm. At idle, vacuum is probably 20 inches. You accelerate. Vacuum drops to 5 or 10 inches. Blend door opens due to loss of vacuum. How much it opens depends on how long you accelerate and how big the pinhole is. Vent temp rises. You stop accelerating, but are going faster, i.e.; higher RPM’s and lower vacuum. Blend door slowly begins to close. Cooling improves.
If you can access the vacuum actuator(s), remove and plug the vacuum line(s). Position the doors for max cooling. Tape them shut and go for a drive.


-------------------------
johnl

mikecap67 on Wed July 14, 2010 3:42 PM User is offlineView users profile

I completely bypassed the heater core and the hot/cold is controlled by cable, so that's not it.

Anyone else have any suggestions? Expansion Valve?? Low charge???

-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

bohica2xo on Wed July 14, 2010 8:12 PM User is offline

Well, 28.5 psi says the POA is working properly. The High side looks low to me, so let's go over what the system is...

OEM this was a tube & fin condensor with a mechanical fan. You are running electric fans, has the condensor been changed?

The OEM condensor fed a receiver/dryer equipped with a sightglass - what does your sightglass look like when the system is running?

The R/D fed a TXV at the evaporator. The TXV has a sensing bulb that is clamped metal-to-metal on the side of the evaporator suction line before the POA. It should be located on the side, either 3 o'clock or 9 o'clock. Not on the top or bottom. It should be insulated with presstite tape so that it only senses line temperature.

The OEM compressor is an A6 unit. Are you still running the A6?

Have you serviced any components in the system recently? How much refrigerant is in the system? How much oil?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mikecap67 on Thu July 15, 2010 1:53 AM User is offlineView users profile

Quote
Originally posted by: bohica2xo
Well, 28.5 psi says the POA is working properly. The High side looks low to me, so let's go over what the system is...
OEM this was a tube & fin condensor with a mechanical fan. You are running electric fans, has the condensor been changed?
The OEM condensor fed a receiver/dryer equipped with a sightglass - what does your sightglass look like when the system is running?
The R/D fed a TXV at the evaporator. The TXV has a sensing bulb that is clamped metal-to-metal on the side of the evaporator suction line before the POA. It should be located on the side, either 3 o'clock or 9 o'clock. Not on the top or bottom. It should be insulated with presstite tape so that it only senses line temperature.
The OEM compressor is an A6 unit. Are you still running the A6?
Have you serviced any components in the system recently? How much refrigerant is in the system? How much oil?
B.

Condenser is stock, reciever dryer/ex valve/compressor changed 3 years ago (no sight glass, olds didn't). Expansion valve was changed (bought it here) and the sensing bulb is clamped at about 5 oclock (tight clamp/cleaned line when installed) and wrapped in the black tar tape.
Compressor changed (stock A6 bought here also) with exp valve and receiver dryer. System hasn't been touched in 3 years (when components were installed) except we added 1/2 -3/4 lb r-12 last weekend to see if it changed anything. (not sure how much oil)

Whats frustrating is if I go start the car and let it idle w/the ac on recirc, fan on low the duct temp will drop to the LOW 40's in about a min or so, even when its 85 outside. If i crank the fan to high, the temp will go into the high 40's (still idling).

Back out of the driveway and pull away and the duct temp immediately climbs to the mid 60's or even higher.

Our heating and cooling guy (only does commercial stuff and our Ice cream machines BTW) really thinks its the expansion valve, but I really thought I would try here first since you guys just do auto stuff.

-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

Edited: Thu July 15, 2010 at 1:57 AM by mikecap67

bohica2xo on Thu July 15, 2010 2:42 AM User is offline

Like I said, the high side is really low. There are 3 possibilities.

1) It is undercharged.

2) The TXV is not working properly, or has an inlet screen full of junk.

3) The evaporator core is being bypassed with airflow in some way. Foam seals deteriorate, etc. The evaporator could be filthy as well - how is the vent airflow?

Are you sure it does not have a sight glass? I am not an olds expert, but every GM car I worked on back then had one. My 1973 Buick sure did. I have heard the "no sight glass" complaint before. Brand new dryers still have sight glasses, and people keep trying to tell me that the are not there anymore. Here is why:




This is a brand new dryer, shipped from AMA about a week ago. No sight glass right?





Wait - what is that? It looks like masking tape, painted the same color as the dryer!



Huh. It really does have a sight glass.

Have a close look at your unit. It may indeed have a sight glass.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Dougflas on Thu July 15, 2010 5:46 AM User is offline

First thing I noticed was indication of low charge. I also agree with bohica2xo that you're low on charge and there is a sightglass. If you really have no sightglass, change the drier for one that has a sightglass, charge it up until the glass clears, add 2 more oz of r12 and you'll be fine. As mentioned, older vehicles have foam surrounding the evaps, on blend doors that deteriorate.

mikecap67 on Sat July 17, 2010 2:51 AM User is offlineView users profile

Thanks bohica2xo, it ended up being low. I dont have an accurate scale, just the digital bathroom one that only reads in 1/2 lbs, but it took 1 lb. The site glass was there also under the paint.

Today it was 92 degrees and after charging my high side reading at 2200 rpm was 180 and the low got up to 30 (did I overcharge alittle?? ) The duct temp on the 40 mile drive to work (93 degrees) NEVER went above 52 with the fan on high. On low it was 41, med was 43. On the drive home at midnight it was 75 degrees and on low/med fan the duct temp stayed rock solid at 41. When I got home I popped the hood and the POA and suction line on the back of the compressor were ICED over, so im wondering if I overcharged?

Thanks Guys.

-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

bohica2xo on Sat July 17, 2010 3:08 AM User is offline

You are welcome.

Charge looks good. The ice on the suction is normal when loads are light.

Once the sight glass is clear, there is room for extra refrigerant in the system. Those systems are large, and hold some reserve refrigerant. People have forgotten that, and tend to undercharge them. "Five Pounds" of refrigerant just does not sound right to people who have been working on 22 ounce hondas...

Glad you got it squared away. Nice car for an 80 mile daily drive.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mikecap67 on Sat July 17, 2010 2:59 PM User is offlineView users profile

Thanks. I don't drive it every day, but as often as i can. (older pic)








-------------------------
72 Cutlass 455

Gunnery Sergeant USMC (Retired 2007)

Edited: Sat July 17, 2010 at 3:01 PM by mikecap67

bohica2xo on Sat July 17, 2010 3:55 PM User is offline

Ok, now I am just jealous.

Nice ride.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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