Fixing A/C? Not sure to to do next
Thread Starter
Race Director
Joined: Mar 1999
Posts: 12,597
Likes: 237
From: Bartlett Illinois
Fixing A/C? Not sure to to do next
The A/C in my 90 (LT5) is weak.. It struggles to stay cold, I also seem to have very weak airflow.
Here is what I have done so far:
- Replaced compressor
- New Accumulator
- New Condenser (Parallel flow, not tube & fin)
- pulled vacuum, verified vacuum held
- Charged with R12
- replaced Blower motor and cage from a 96
- Blower Resistor module (I have C60)
Not sure what to do next. I did readjust the Blend door to confirm it is closing all the way on cold. I need to tke the blower back out and see if I visually inspect the Evaporator before I decide to pull the heater case apart and clean it
I know I have 3 things going against me:
1) LT5 motor produces more heat
2) 10PA17 vs 10PA 20 compressor (20 is too big to fit with LT5, 17 is stock)
3) no longer have the ZR-1 specific windshield
How do I get more air flow out of it, it just seems really weak compared to what I remember on my 89
Here is what I have done so far:
- Replaced compressor
- New Accumulator
- New Condenser (Parallel flow, not tube & fin)
- pulled vacuum, verified vacuum held
- Charged with R12
- replaced Blower motor and cage from a 96
- Blower Resistor module (I have C60)
Not sure what to do next. I did readjust the Blend door to confirm it is closing all the way on cold. I need to tke the blower back out and see if I visually inspect the Evaporator before I decide to pull the heater case apart and clean it
I know I have 3 things going against me:
1) LT5 motor produces more heat
2) 10PA17 vs 10PA 20 compressor (20 is too big to fit with LT5, 17 is stock)
3) no longer have the ZR-1 specific windshield
How do I get more air flow out of it, it just seems really weak compared to what I remember on my 89
Pro
Joined: Jan 2011
Posts: 580
Likes: 8
From: Clemson SC
I don't claim to be an expert but have you put a set of gauges on it and gotten the numbers. That is usually the first step in any A/C diagnosis and can provide a lot of info to save putting on the wrong parts.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
The A/C in my 90 (LT5) is weak.. It struggles to stay cold, I also seem to have very weak airflow.
Here is what I have done so far:
- Replaced compressor
- New Accumulator
- New Condenser (Parallel flow, not tube & fin)
- pulled vacuum, verified vacuum held
- Charged with R12
- replaced Blower motor and cage from a 96
- Blower Resistor module (I have C60)
Not sure what to do next. I did readjust the Blend door to confirm it is closing all the way on cold. I need to tke the blower back out and see if I visually inspect the Evaporator before I decide to pull the heater case apart and clean it
I know I have 3 things going against me:
1) LT5 motor produces more heat
2) 10PA17 vs 10PA 20 compressor (20 is too big to fit with LT5, 17 is stock)
3) no longer have the ZR-1 specific windshield
How do I get more air flow out of it, it just seems really weak compared to what I remember on my 89
Here is what I have done so far:
- Replaced compressor
- New Accumulator
- New Condenser (Parallel flow, not tube & fin)
- pulled vacuum, verified vacuum held
- Charged with R12
- replaced Blower motor and cage from a 96
- Blower Resistor module (I have C60)
Not sure what to do next. I did readjust the Blend door to confirm it is closing all the way on cold. I need to tke the blower back out and see if I visually inspect the Evaporator before I decide to pull the heater case apart and clean it
I know I have 3 things going against me:
1) LT5 motor produces more heat
2) 10PA17 vs 10PA 20 compressor (20 is too big to fit with LT5, 17 is stock)
3) no longer have the ZR-1 specific windshield
How do I get more air flow out of it, it just seems really weak compared to what I remember on my 89
1. Measure your air temps exiting the vents -should be ~40 -50*F or so, and if it is,
2. Investigate the blendair doors and linkages. On my '92 (base controls and LT1 engine), the adjustment at the crank arm for the hot/cold blend door was off so the door would get all the way to the cold position; some hot air always leaked in. Now that wouldn't affect air flow VOLUME, but it's something to look at...especially when you feel you're having issues w/air flow in the HVAC system. I've also noticed on both my 'Vette and my Silverado, air flow seems to decrease when I use "recirculate". Therefore, I never use that feature unless I'm behind a Diesel truck that's "Rolling Coal".
Thread Starter
Race Director
Joined: Mar 1999
Posts: 12,597
Likes: 237
From: Bartlett Illinois
Yes I have had gauges on.. need to check again.. it is on my list..
Temp gauge showed 50 out the vent in my driver on a 77 deg day.. hotter the outlet temperature rises..
I will pull the blower and inspect the evaporator too.. Recirc or no recirc the air flow is weak.. my malibu ss with auto ac has more power out the vent at setting #2 from off..
Still need to just get some time to work on it
Temp gauge showed 50 out the vent in my driver on a 77 deg day.. hotter the outlet temperature rises..
I will pull the blower and inspect the evaporator too.. Recirc or no recirc the air flow is weak.. my malibu ss with auto ac has more power out the vent at setting #2 from off..
Still need to just get some time to work on it
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Yes I have had gauges on.. need to check again.. it is on my list..
Temp gauge showed 50 out the vent in my driver on a 77 deg day.. hotter the outlet temperature rises..
I will pull the blower and inspect the evaporator too.. Recirc or no recirc the air flow is weak.. my malibu ss with auto ac has more power out the vent at setting #2 from off..
Still need to just get some time to work on it
Temp gauge showed 50 out the vent in my driver on a 77 deg day.. hotter the outlet temperature rises..
I will pull the blower and inspect the evaporator too.. Recirc or no recirc the air flow is weak.. my malibu ss with auto ac has more power out the vent at setting #2 from off..
Still need to just get some time to work on it
50* on a 77* day is pretty warm, and an air flow restriction. On "vent", it should blow like a sone-of-a-bee on high.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Did you replace the orifice tube? We need your numbers while the engine was turning at least 12-1500 RPM. How did you add the R12, by weight or running pressure's? an over charge could cause these symptoms. Have you tried connecting the Blower motor directly to the battery to see if this helps to speed the motor up, maybe the motor has an bearing or armature problem..
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Did you replace the orifice tube? We need your numbers while the engine was turning at least 12-1500 RPM. How did you add the R12, by weight or running pressure's? an over charge could cause these symptoms. Have you tried connecting the Blower motor directly to the battery to see if this helps to speed the motor up, maybe the motor has an bearing or armature problem..
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 764
I was going to suggest the orifice tube also. That's basically the most important thing that effects how well it cools since that's what makes it an air conditioner in the first place. You might want to google variable air conditioner orifice and see if theres one that fits your car. Makes a huge difference in performance on some Ive done before.
- good point to bring up. I did a quick search for a VOT, and came up with this -it says it fits both my 85 and 90 corvettes. since I'm rebuilding the AC in my 85 and converting to 134a, i have a new fixed tube in my shopping cart - might as well replace the fixed with the variable -
if anyone is not familiar with the variable vs. the fixed thing, here's some easy reading -
http://www.freeasestudyguides.com/fi...fice-tube.html
Last edited by Joe C; Jul 14, 2015 at 06:22 AM.
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Thread Starter
Race Director
Joined: Mar 1999
Posts: 12,597
Likes: 237
From: Bartlett Illinois
I am quite sure I swapped the oriface tube. Anyway. I will get gauages on it for the cooling portion.
That still does not explain the weak volume of air.. It is weak no matter what mode
That still does not explain the weak volume of air.. It is weak no matter what mode
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 764
Team Owner
Joined: Sep 2003
Posts: 25,406
Likes: 2,744
There are multiple foam seals between the various sections of the ductwork in the dash and evaporator cases. It doesn't take much of a leak to effect volume. I wouldn't be surprised if there's also a leak under the hood at the evaporator tubes. That requires a seal by using refrigeration tape. The valves(doors)also are very likely not sealing well to the ducts.
You could also confirm the voltage available to the motor with the various speeds. A simple jumper and a volt meter. Maybe just an older motor could also contribute to decreased performance. I don't know that you could rely on an amperage check to evaluate it but maybe.
You could also confirm the voltage available to the motor with the various speeds. A simple jumper and a volt meter. Maybe just an older motor could also contribute to decreased performance. I don't know that you could rely on an amperage check to evaluate it but maybe.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Jeff, Here is a simple guide on how to read your High/Low pressures,
Your FSM will have the more specific performance pressure's based on OAT, Humidity etc. so this is only a simple guide..
http://www.vintageair.com/DownloadsS...ng%20Guide.pdf
Your FSM will have the more specific performance pressure's based on OAT, Humidity etc. so this is only a simple guide..
http://www.vintageair.com/DownloadsS...ng%20Guide.pdf
Thread Starter
Race Director
Joined: Mar 1999
Posts: 12,597
Likes: 237
From: Bartlett Illinois
Some findings..
Car has been in garage all week.. temperature was about 88 Deg ( using IR temp gun on walls and other items)
Hooked up gauges, Started car, turned A/C on (NO recirc), Fan was on low speed.
Vent Temperature got down to ~44 degs..
Low side pressure hovered around 28psi, high side went from 200 to 250, then the fan kicked on and it dropped to 200 again, when fan turned off the scenario repeated
I did not try it at 1500 and I did not have a fan to push air to the car.. I know that is what should be done, but I wanted to see if the system works.. apparently it does
I did notice the Evaporator box was col to the touch so the insulation of the box itself is not very good.. what can I add to it to help keep the cool in and the heat out?
Car has been in garage all week.. temperature was about 88 Deg ( using IR temp gun on walls and other items)
Hooked up gauges, Started car, turned A/C on (NO recirc), Fan was on low speed.
Vent Temperature got down to ~44 degs..
Low side pressure hovered around 28psi, high side went from 200 to 250, then the fan kicked on and it dropped to 200 again, when fan turned off the scenario repeated
I did not try it at 1500 and I did not have a fan to push air to the car.. I know that is what should be done, but I wanted to see if the system works.. apparently it does
I did notice the Evaporator box was col to the touch so the insulation of the box itself is not very good.. what can I add to it to help keep the cool in and the heat out?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
No worries. Others will probably have better advice, but what I was thinking was that (for example) your evap outlet pipe temps was 35*, and your vent temp is 44 (fan on low) then I'd be thinking that you're blending warm air in, unintentionally.
You're pressures don't seem bad to me. R12 AC is not my forte' though, so if a more knowledgeable poster says my theory is FOS, listen to them.
You're pressures don't seem bad to me. R12 AC is not my forte' though, so if a more knowledgeable poster says my theory is FOS, listen to them.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Jeff, your numbers appear to be Nominal, and this test was done at idle? if so, I would say your A/C work is spot on! The High pressure reading should be 2 X ambient + 15% this comes out to [202.4] psi at High idle with forced air.. you Observed [200-250] without forced air, the pressure dropped when the Fan kicked in so this indicates the Condenser is doing it's job.
Tom is right! in order to Quantify how much Liquid Freon is boiling inside of the Evaporator ( full, half full) you measure the temperature of the Inlet/Outlet pipes. The outlet pipe should be near the same temperature as the inlet tube.. read "If 30 PSI is a good low side pressure, then why isn't the system cooling?" in the following link.
http://aircondition.com/tech/questio...ith-Gauges-FAQ
Tom is right! in order to Quantify how much Liquid Freon is boiling inside of the Evaporator ( full, half full) you measure the temperature of the Inlet/Outlet pipes. The outlet pipe should be near the same temperature as the inlet tube.. read "If 30 PSI is a good low side pressure, then why isn't the system cooling?" in the following link.
http://aircondition.com/tech/questio...ith-Gauges-FAQ
Last edited by desertmike1; Jul 16, 2015 at 12:28 AM.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Jeff, one more thing to conceder during your troubleshooting; A few years ago I resealed a 10PA17 Compressor in my Honda, and while pouring over Data I discovered that the [17] Suffix in the Model number indicates BTU x 1K [17,000 BTU] according to the Honda Specifications Manual.
This being said; tells me that the LT5 vettes suffer 3K Btu less then the LT1 vettes that are equipped with an 10PA20 Compressor. Kind of like replacing your home air conditioner with a smaller unit! If this is true then your Vette will suffer slightly, with the same amount of sun radiation coming through the Glass, of one car verse's the other.
Just a thought..
This being said; tells me that the LT5 vettes suffer 3K Btu less then the LT1 vettes that are equipped with an 10PA20 Compressor. Kind of like replacing your home air conditioner with a smaller unit! If this is true then your Vette will suffer slightly, with the same amount of sun radiation coming through the Glass, of one car verse's the other.
Just a thought..