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A/C charged, compressor turning: warm air

I'm sure everyone is tired of A/C threads, but I've gone through the search function and the Griffiths troubleshooting guide, and am stumped.

1988 Carrera Cabriolet. Had a R-134 conversion a few years ago, including barrier hoses, expansion valve, drier, etc. Ran great until this summer.

System was blowing warm air (84* on a 95* day), so I assumed it needed a charge -- it hasn't had one in over two years.

Hooked up the gauges, and it was a little low, but it took less than a can to get the pressures to 35 low side & 200 high side.

Compressor clutch engages when you turn on the thermostat, and the compressor seems to be generating appropriate pressures -- but the air coming out is warm: 84-88 degrees.

All the fans seem to be working. Fuses and relay are good.

Any suggestions on what may be wrong?

Thanks!
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Old 06-29-2018, 04:57 PM
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This is a real mystery (to me) - have never seen a system with appropriate range pressure that is blowing warm air.

This is probably a silly question, as you appear to know what you are doing, but when you saw those gauge reading was the deck lid closed (or maybe you have installed a fan on the tail condenser, like I have) so that air was being drawn over the condenser? If not, you will see higher than you should pressures for the amount of refrigerant in the system.

One thing worth checking is to remove the evaporator intake duct, behind the passenger floorboard, and see if the bottom of the evaporator is clogged up with mold and/or debris of some sort (leaves, carpet fiber, etc).

Last edited by Rawknees'Turbo; 06-29-2018 at 08:21 PM..
Old 06-29-2018, 08:18 PM
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In the smugglers box, Is the line going into the evaporated cold?
Old 06-30-2018, 03:34 AM
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Quote:
Originally Posted by COLB View Post
I'm sure everyone is tired of A/C threads, but I've gone through the search function and the Griffiths troubleshooting guide, and am stumped.

1988 Carrera Cabriolet. Had a R-134 conversion a few years ago, including barrier hoses, expansion valve, drier, etc. Ran great until this summer.

System was blowing warm air (84* on a 95* day), so I assumed it needed a charge -- it hasn't had one in over two years.

Hooked up the gauges, and it was a little low, but it took less than a can to get the pressures to 35 low side & 200 high side.

Compressor clutch engages when you turn on the thermostat, and the compressor seems to be generating appropriate pressures -- but the air coming out is warm: 84-88 degrees.

All the fans seem to be working. Fuses and relay are good.

Any suggestions on what may be wrong?

Thanks!
I agree with Ronnie, that with those pressures, you should have cool air. Any chance engine heated hot air is getting into the air stream? Like broken heater cable, maybe. If worse comes to worse, you may need to evacuate and recharge by weight, then check pressures.
Good luck,
Dave
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Old 06-30-2018, 10:39 AM
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Quote:
Originally Posted by Rawknees'Turbo View Post
This is a real mystery (to me) - have never seen a system with appropriate range pressure that is blowing warm air.

This is probably a silly question, as you appear to know what you are doing, but when you saw those gauge reading was the deck lid closed (or maybe you have installed a fan on the tail condenser, like I have) so that air was being drawn over the condenser? If not, you will see higher than you should pressures for the amount of refrigerant in the system.

One thing worth checking is to remove the evaporator intake duct, behind the passenger floorboard, and see if the bottom of the evaporator is clogged up with mold and/or debris of some sort (leaves, carpet fiber, etc).
Thanks for the replies -- No fan, and I had the trunk lid closed (somewhat cracked though, to allow the hoses to thread through.

I will check the smuggler's box and evaporator intake and see if something is jacked there. Hard to believe it is anything to do with the expansion valve, as it is relatively new, and has functioned well for 3+ years. We've had some mice in the garage, and it is conceivable some built a nest in there over the winter.

If there is nothing in the box, and it is still blowing warm, I will evacuate the whole thing, pull a vacuum, and try to refill.
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Old 06-30-2018, 01:58 PM
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I've had poor luck adding r-134, best to pull it all out and recharge from scratch with proper amount by capacity. It's not like r-12 as overcharge is as bad as undercharge.
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Old 06-30-2018, 02:00 PM
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Possible hose disconnect between evap plenum and vent ducts either at plenum and/or at vent duct side---is pushing warm air in from smugglers. Or, maybe evap's intake side is clogged (been there.) Seems in either of these cases you might sense a difference either in air volume or sound from vents.

Agree with RonO that this is mysterious.

... Answer will come when Charlie gets here.
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Old 06-30-2018, 02:17 PM
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Quote:
Originally Posted by COLB View Post
If there is nothing in the box, and it is still blowing warm, I will evacuate the whole thing, pull a vacuum, and try to refill.
I would do this anyways after some vetting, even if nothing is found.

Quote:
Originally Posted by RSTarga View Post
I've had poor luck adding r-134, best to pull it all out and recharge from scratch with proper amount by capacity. It's not like r-12 as overcharge is as bad as undercharge.
+1

Got sloppy last week and "added a can" of R-134 to my 2004 RAV4. Vents weren't nippy enough. It has a 16 to 20oz capacity. Bad move. More delicate than the old 911. High limit switch was cycling from overfill.

Started over with a 30lb tank and gauges. Oh, and a scale.
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Old 06-30-2018, 02:26 PM
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Opened up the smuggler's box.

The air coming out of the blower (where my hand is) is only slightly colder than ambient - so it is not any issue with an air blockage or blending hot air with the cold:



The pipe leading to the expansion valve is cold (where the thermostat bulb is located), so the system is functioning in some degree. It appears there is a problem in the evaporator itself: the refrigerent is not cooling any air in the evaporator.

I guess I am going to purge the system and pull the evaporator and see what it looks like. What I expect is that it is coated with gunk and either needs to be cleaned or replaced.

Would a gummed up evaporator lead to the symptoms of my system?
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Old 06-30-2018, 05:34 PM
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The bottom of the evaporator can get gunked up with debris over the years. Something you might expect to have a gradual decrease in performance and not a sudden loss. Does the air flow thru the vents feel restricted? If in the end you wind up pulling it, I would just replace it.
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Old 07-01-2018, 02:35 AM
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Quote:
Originally Posted by walt View Post
The bottom of the evaporator can get gunked up with debris over the years. Something you might expect to have a gradual decrease in performance and not a sudden loss. Does the air flow thru the vents feel restricted? If in the end you wind up pulling it, I would just replace it.
No - the air flow is good.

The loss could have been gradual -- I drive with the top down 90% of the time, and have not tried to drive the car in the heat of Texas summer the past few years.

I'm leaning toward to "replacement" course of action, but am not excited about the $500 for the Kuehl kit, which is pretty much the only option since Rennaire has gone out of business. It is certainly cheaper than Porsche OEM -- and their products have a good reputation, it is just a lot of money for a capability I don't use much.
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Old 07-01-2018, 04:10 AM
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Quote:
Originally Posted by COLB View Post
I guess I am going to purge the system and pull the evaporator and see what it looks like. What I expect is that it is coated with gunk and either needs to be cleaned or replaced.

Would a gummed up evaporator lead to the symptoms of my system?
Rather than pulling evap to see if it's dirty, it's possible to look at bottom by removing passenger's foot rest and then removing gizmo that's mounted in passenger's side intake. Put smart phone inside and shoot pic of evap's bottom. Bob suggested I do this and it was very enlightening.

Dirty evap does lead to loss of cooling but as Walt noted it would probably be gradual loss---unless there was an "event" that instantly lead to a great deal of debris in car and much got sucked into plenum.
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Old 07-01-2018, 04:11 AM
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Sounds like you may possibly have moisture in the system. Remove the refrigerate go find you a vacuum pump, an A/C or refrigeration service guy would have one. Install your gauges on high and low side,center hose to pump. Try and pull inchs of vacuum on your suction gauge for a few hours. Then close of your gauges and see if system will hold the vacuum. If it want you probably have a pretty good leak somewhere. But this process should have removed the moisture that is effectiving the orifice in your explansion valve. Add fresh 134 back to system. Charge with hood down so rear condenser can do itís job . On your gauges they should be a scale inside of pressure numbers . They are specific to refrigerate evaporate temps. The scale usually has noted refrigerate types find the one for 134a. You want your pressure to match the temperature your trying to achieve in your evaporator. So letís say your looking for a 35 degree evaporator. Then you calculate a 10 degree differential across evaporator to give you 45 degree air coming out your vents. So what ever suction pressure gives you that number on the gauges
Hope this helps
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Old 07-01-2018, 04:49 AM
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Hasn't been mentioned, poor condensing capacity. Check that the front condenser blower is blowing through. Just feel for hot air blowing under the front rock guard. I don't see how moisture can get into a pressurized closed system.
Also, even though the pressure is in the ballpark it might still be low in 134, you can add some more see what happens before removing all the 134 and starting with an empty system.
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Old 07-01-2018, 06:58 AM
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When you have these pressures:
"the pressures to 35 low side & 200 high side."
when it is operating....
How many seconds does it take for the high and low side to rebalance at say 110psi when you turn off the AC and the refrigerant passes thru the TEV to balance both sides out.
Is it real fast?
Or slow in?
In seconds?
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Old 07-01-2018, 07:21 AM
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It depends on amibient conditions, refrigerates expand and contract under pressure and ambient conditions, it’s a realative small system however again depends on conditions. It could be a few minutes or more
Thanks
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Old 07-01-2018, 08:08 AM
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Maybe COLB's pressure is equalizing in 2-3 seconds.
I was asking him for his situation.
What would that tell you?
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Old 07-01-2018, 08:15 AM
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Quote:
Originally Posted by macssc911 View Post
It could be a few minutes or more
I would like to hear the response to tsuter's question out of curiosity.

Side bar: Does macs in macssc911 stand for Mobile Air Conditioning Society or are you Mac?

I was impressed to see your description of the gauge face scale for R-134. I did pass the MACS EPA 609 test back in the late 90's but I do not remember reading about the gauge dial scales.

The guys here talk about using pressure readings when filling. They must be using the R-134 scale?
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Old 07-01-2018, 08:55 AM
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If it is equalizing that quickly I would guess the superheat setting on expansion valve is non existent, or valve is opened up all the way, the key to setting superheat on X valve if you donít have a superheat meter, is to adjust slowly about 1/2 turn at a time. It usually takes 10 minutes or so for valve to react to the adjustment. It is a TXV the bulb has to have time to let the gas in the cap tube to expland or contract as it adjust to the temperature of the suction line. Itís a slow process, the end result is to flood the evaporator and no more. You are looking for temperature differential of about 10 degrees from the center of the evaporator to the end where suction line connects
If valve is opened all the way up the liquid refrigerate is not able or boil under pressure in evaporator it just flows through and the evaporator cannot obtain proper temperature to perform
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Old 07-01-2018, 08:59 AM
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Quote:
Originally Posted by macssc911 View Post
If it is equalizing that quickly I would guess the superheat setting on expansion valve is non existent, or valve is opened up all the way, the key to setting superheat on X valve if you donít have a superheat meter, is to adjust slowly about 1/2 turn at a time. It usually takes 10 minutes or so for valve to react to the adjustment. It is a TXV the bulb has to have time to let the gas in the cap tube to expland or contract as it adjust to the temperature of the suction line. Itís a slow process, the end result is to flood the evaporator and no more. You are looking for temperature differential of about 10 degrees from the center of the evaporator to the end where suction line connects
If valve is opened all the way up the liquid refrigerate is not able or boil under pressure in evaporator it just flows through and the evaporator cannot obtain proper temperature to perform
I don't see anything on my expansion valve that is adjustable.
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Old 07-01-2018, 09:33 AM
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