Air conditioning Evaporator Freezing Up - CorvetteForum - Chevrolet Corvette Forum Discussion



C4 Tech/Performance
L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Air conditioning Evaporator Freezing Up

Reply
 
 
 
Thread Tools Search this Thread
Old 07-14-2017, 08:49 PM   #1
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default Air conditioning Evaporator Freezing Up

I'm having an issue with my 96 vert. The a/c starts off fine with the air blowing out of the vents at full force and cold. After driving for an hour or more the force of the air coming out of the vents is diminished to what feels like 1/4 of the force. I noticed the line from the accumulator to the evaporator is frozen with hard white ice. I've changed the cycling switch since it appears the compressor never cycles. I've checked the controller for codes and it's only 00. I've put gauges on it and it's about 23-25 on the low side and about 180-190 on the high side at about 68% humidity and 80 degrees. Is the system low on freon? Is there something else I'm missing?
ajd3rd is offline   Reply With Quote
Old 07-14-2017, 09:08 PM   #2
xrav22
CF Senior Member
 
xrav22's Avatar
 
Member Since: Mar 2013
Location: Canoga Park Cali.
Posts: 908
Thanked 65 Times in 63 Posts
Default


Here is a chart I use to convert to 134. It looks like you are low on Freon by 1/2 12 oz can. I am not an expert but I have the gauges and my pressures were correct for 90 degrees.
If you are freezing up there would have to be moisture in the system, has it been open for an extended period of time? Also I was happy to see on first test my fans were coming on when ac is on if yours are not after warm up could present a problem.
xrav22 is online now   Reply With Quote
Old 07-14-2017, 09:22 PM   #3
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

Thanks for the reply. The system hasn't been open to my knowledge. It seemed ok earlier in the year. The car has 40k miles. It's a 96 so it came with 134a. The fsm called for 28 psi on the low side. Do you think 23 -25 is low enough to cause the freezing and non cycling of the compressor?
ajd3rd is offline   Reply With Quote
Old 07-14-2017, 09:44 PM   #4
xrav22
CF Senior Member
 
xrav22's Avatar
 
Member Since: Mar 2013
Location: Canoga Park Cali.
Posts: 908
Thanked 65 Times in 63 Posts
Default

I noticed my ac delco conversion does not really cycle all that much when it is on. I'm thinking you are mabey low 1 12 oz can causing Freon to over cool and not work properly. I would add to the correct psi and see how it works, wearing protection of course.
I wanted to edit the psi can only be determined by outside temp.

Last edited by xrav22; 07-15-2017 at 08:50 PM.
xrav22 is online now   Reply With Quote
Old 07-14-2017, 11:32 PM   #5
pcolt94
CF Senior Member
 
pcolt94's Avatar
 
Member Since: Jan 2006
Location: Orlando FL
Posts: 5,037
Thanks: 0
Thanked 56 Times in 53 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
Thanks for the reply. The system hasn't been open to my knowledge. It seemed ok earlier in the year. The car has 40k miles. It's a 96 so it came with 134a. The fsm called for 28 psi on the low side. Do you think 23 -25 is low enough to cause the freezing and non cycling of the compressor?
The cycling switch should open at 22.5 psi and close at 46 psi. It will cycle at the same pressures always. Higher ambient and engine temps will cause it to cycle less as it will be harder to get down to the 22.5 with higher Freon temps.

Now if the system is low on Freon it will cycle more (short cycle) and the evaporator can freeze up. If it short cycles thatís an indication it is low on Freon.

If the low side goes much lower than 22.5 like 18 or 20 it can freeze up if it does not cycle.

When you first start the car, AC to max, fan to 10, how often does the compressor cycle?
pcolt94 is offline   Reply With Quote
Old 07-15-2017, 12:32 AM   #6
Hot Rod Roy
CF Senior Member
 
Hot Rod Roy's Avatar
 
Member Since: Sep 2004
Location: Mission Viejo CA
Posts: 1,933
Thanked 137 Times in 127 Posts
Default

Quote:
Originally Posted by xrav22 View Post
If you are freezing up there would have to be moisture in the system,
The "freezing up" he's seeing is on the outside of the tubes! If he had moisture in the system, the a/c would quit working because of the moisture freezing on the inside of the system. Moisture in the system is not the problem.

Hot Rod Roy is online now   Reply With Quote
Old 07-15-2017, 07:29 AM   #7
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

The compressor is not cycling. I've already changed the cycling switch but the compressor continues to run all the time. I tried pulling the wiring plug from the cycling switch and that disengaged the clutch so it seems the wiring is good. The only other thing I can think of is the new cycling switch is defective.
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 07:50 AM   #8
WVZR-1
CF Senior Member
 
Member Since: Sep 2003
Location: Charles Town WV
Posts: 15,319
Thanked 648 Times in 626 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
The compressor is not cycling. I've already changed the cycling switch but the compressor continues to run all the time. I tried pulling the wiring plug from the cycling switch and that disengaged the clutch so it seems the wiring is good. The only other thing I can think of is the new cycling switch is defective.
Why wouldn't you go directly to the FSM diagnostics for "COMPRESSOR ALWAYS ENGAGED" - That seems to be a relatively sure way to deal with your particular issue.

8A-67-5 in the FSM

Sometimes those diagnostic trees seem foolish and many times maybe are but in your case I'd think a very good direction to head towards.

I assumed this is a C68 car - if the car is a C60 then it's very different!
WVZR-1 is online now   Reply With Quote
Old 07-15-2017, 08:11 AM   #9
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

Wvzr-1. I've looked at the fsm. I'm unsure what wire to disconnect when it says to remove blower wire. I'll take another look this morning. Thanks.
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 08:24 AM   #10
WVZR-1
CF Senior Member
 
Member Since: Sep 2003
Location: Charles Town WV
Posts: 15,319
Thanked 648 Times in 626 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
Wvzr-1. I've looked at the fsm. I'm unsure what wire to disconnect when it says to remove blower wire. I'll take another look this morning. Thanks.
In the "ALWAYS ON" I don't see any reference to "blower wire".

Is it actually "ALWAYS ON"? C68 or C60?
WVZR-1 is online now   Reply With Quote
Old 07-15-2017, 08:33 AM   #11
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

It's a C68
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 08:46 AM   #12
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

WVZR-1. I was looking in the a/c section of the fsm. I'll get the other book and take a look shortly. Thanks for the help. I'll post an update once I go through the page you recommended. Thanks!
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 09:16 AM   #13
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

I should clarify the compressor clutch is always engaged when the a/c is on but not when the a/c is off. I'm going through the fsm for the c68 and so far everything checks out but I now need to pull the control head. My question is when the service manual say clutch always engaged does that mean only when a/c is on or that the clutch is engaged even with a/c off?
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 09:34 AM   #14
ihatebarkingdogs
CF Senior Member
 
Member Since: Nov 2016
Location: Torrance CA
Posts: 368
Thanked 58 Times in 55 Posts
Default

I've never seen evaporator freeze-up in a CCOT system caused by low refrigerant. Nor do I think it CAN be caused by low refrigerant. Here's why: If the refrigerant charge is low, when the compressor turns on, the low-side will be quickly pulled down to the turn-off setting of the cycling switch. The lower the charge, the shorter the on time, and longer the off time of the cycling. The FSM details this as a check for "low refrigerant level".


Actually, regardless of charge, the cycling switch should turn off the compressor when the low side pressure is just above the temperature that freezing occurs. If the evaporator is freezing, the compressor is not turning off at the appropriate low side pressure.


The freezing evaporators because of low charge occurs in home systems that use capillary tube refrigerant metering.
ihatebarkingdogs is offline   Reply With Quote
Old 07-15-2017, 09:43 AM   #15
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

Thanks for the info. The pressures seem close to what the FSM is calling for so that's probably not it. I guess I'll pull the dash apart to get the head unit out and try disconnecting it. As I posted earlier the only thing I'm not sure of is what the fsm means when it says clutch always on. Is that on constantly when the a/c is on or is it stuck on even when ac is off?
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 10:25 AM   #16
ihatebarkingdogs
CF Senior Member
 
Member Since: Nov 2016
Location: Torrance CA
Posts: 368
Thanked 58 Times in 55 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
I'm not sure of is what the fsm means when it says clutch always on. Is that on constantly when the a/c is on or is it stuck on even when ac is off?
It can mean both.

The clutch should of course NOT be on when the system is in a mode that does NOT call for the compressor.

The other circumstance is that the clutch should not be on if the pressure gets to the minimum low side pressure where icing can occur. This is "checked" by running the system with a pressure gauge on the low-side under low heat-load (low blower speed usually works) and observing that the compressor cycles off when the low side pressure is equivalent to about 33-34 deg F. (I don't have a pressure chart in front of me, and I've learned to not guess on CF, as if you're off by a degree, you'll be called-out for it).

There are also inputs for high-pressure protection that turn off the compressor clutch. Generally these strategies are in place for a loss of cooling fan operation at low speeds which will cause dangerous high-side pressures.

Conclusion: You don't want the clutch engaged when the mode doesn't call for it. It must cycle off when minimum evaporator temperature is reached. And it cycles off to prevent dangerous high -side pressures.

Last edited by ihatebarkingdogs; 07-15-2017 at 10:28 AM.
ihatebarkingdogs is offline   Reply With Quote
Old 07-15-2017, 10:45 AM   #17
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

Thanks for the reply. If my thinking is correct, if I set the a/c on auto and turn the temp up to 90 the compressor should shut off? I'm going to try that now before I pull the head unit out.
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 10:54 AM   #18
ajd3rd
CF Member
Thread Starter
 
Member Since: Feb 2004
Location: Bloomingburg NY
Posts: 70
Thanked 1 Time in 1 Post
Default

ok, car a/c on auto a/c temp set to 90, outside temp is 77 and compressor runs continuously. I assume I need to pull the head and see if it disconnects when I disconnect the head. Any input would be greatly appreciated.
ajd3rd is offline   Reply With Quote
Old 07-15-2017, 11:00 AM   #19
ihatebarkingdogs
CF Senior Member
 
Member Since: Nov 2016
Location: Torrance CA
Posts: 368
Thanked 58 Times in 55 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
if I set the a/c on auto and turn the temp up to 90 the compressor should shut off?
I honestly don't know about the "90" thing. I just did Operations check at NCRS Nationals on 7 90-96 C4's. I have the owner run the temp to 60, then go accross the buttons. I know the compressor is off in "panel" (dash vents only), "floor" (heater), then comes back on in "defrost". In defrost, I have the owner run the temp to 90 and check that the temp goes up. I have never noticed if the compressor turns off at 90 or not. But it is in "defrost" so perhaps not. I know how I check them for NCRS purposes, but I don't check every corner of the operational parameters.


I know the compressor is OFF in floor / heater. Second button from the right.

Last edited by ihatebarkingdogs; 07-15-2017 at 11:02 AM.
ihatebarkingdogs is offline   Reply With Quote
Old 07-15-2017, 11:02 AM   #20
pcolt94
CF Senior Member
 
pcolt94's Avatar
 
Member Since: Jan 2006
Location: Orlando FL
Posts: 5,037
Thanks: 0
Thanked 56 Times in 53 Posts
Default

Quote:
Originally Posted by ajd3rd View Post
The compressor is not cycling. I've already changed the cycling switch but the compressor continues to run all the time. I tried pulling the wiring plug from the cycling switch and that disengaged the clutch so it seems the wiring is good. The only other thing I can think of is the new cycling switch is defective.
These numbers are normal for an engine that is just sitting and idling.
"I've put gauges on it and it's about 23-25 on the low side and about 180-190 on the high side at about 68% humidity and 80 degrees."

Now connect your gauges again and with AC to MAX, REV the engine to about 1500 or so and hold it there for about 30 seconds and watch the low pressure side. It should come down to 22.5 psi and then cycle (cycle switch opens) and the compressor should stop. The pressure should then rise by itself to 46 psi and re-engage the compressor. This should repeat for an normal system operation.

See what your results are.
If you go much past below 22 psi, possible bad cycle switch.
If you can't get down past 22.5, possible overcharged system.

Other things that will affect system operation is airflow over the condenser. Check for excess leaves and debris on the condenser. Both fans should be operating at low speed with the AC on for a 96vette (check it).
pcolt94 is offline   Reply With Quote
Go Back   CorvetteForum - Chevrolet Corvette Forum Discussion >
Reload this Page
  • Air conditioning Evaporator Freezing Up
  •  
     
    Reply

    Related Topics
    Thread Thread Starter Forum Replies Last Post
    67 factory air problem ohiohotrods C1 & C2 Corvettes 6 09-20-2016 07:51 AM
    At my wits end with a/c problem! cadmaniac C4 Tech/Performance 9 07-29-2015 03:53 PM
    1985 HVAC/Cabin Air issue BigDaddy5 C4 Tech/Performance 13 04-05-2015 09:28 PM
    Another Heat Insulation Consideration - AC Plenum 68/70Vette C3 General 7 07-17-2010 02:58 PM
    Wanted:74 evaporator outlet case Bill Oxley C3 Parts for Sale/Wanted 2 09-23-2004 04:07 PM


    Thread Tools Search this Thread
    Search this Thread:

    Click for Advanced Search

    Posting Rules
    You may not post new threads
    You may not post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are Off
    Pingbacks are Off
    Refbacks are Off

    Forum Jump


    All times are GMT -4. The time now is 02:52 PM.


     
    • Ask a Question
      Get answers from community experts
    Question Title:
    Description:
    Your question will be posted in: