A/C Trouble Shooting Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Sheepdip** · 02-25-2020, 12:09 AM

Ok I'm looking for some suggestions on what's happening here with my A/C system.

I'm leaning towards a bad compressor but I will be taking it to a pro for a second opinion before I cry wolf to the vendor if I can't resolve the issue with some guidance/suggestions from all you smart guy's out there.

History: 1970 GMC... Everything is new, compressor, hoses, condenser, dryer/filter, POA upgrade valve with binary cut out switch, evaporator, expansion valve.

With the exception of the POA upgrade valve all sourced thru LMC Truck.

Today I pulled a vacuum on the new system, pulled right down both sides and held for over an hour with no issues.
Here's where things went south, I started feeding the R134A into the suction side and it went to about 30 psi and climbing right away to about 50 psi and the binary switch kept cycling the clutch out ...high pressure side was almost nothing and remained almost nothing eventually climbing to about 25psi

I then with the engine off I fed some refrigerant thru the high side port and got it up to about 100 psi then shut it down and went back to feeding thru the low port with the compressor engaged, I jumped the binary switch to keep the compressor from cycling in and out and got the low side up to about 70 psi, but I'm assuming all was from can pressure, because my high side is still 100 and never went any higher.

I let it set for about an hour while I scratched my head and tried to figure it out. Rechecked the gauges and still 70psi on the low and 100psi on the high.

It's like the compressor is not processing anything thru it.

I'm open to suggestions if you got any.

**A1971Blazer** · 02-25-2020, 08:17 AM

member F.A.A.benny is the AC guru
haven't seen posts from him in a while though

Kudzupatch · 02-25-2020, 09:16 AM

How much freon have you put in? You didn't say It is normal for it cycle when low and sounds to me from what you have posted you simply don't have enough refrigerant in the system yet.

weq92f · 02-25-2020, 10:28 AM

.
Be sure to put in the right amount of oil. Your compressor may have come with some oil already loaded but your system may call for more.

-klb

**Sheepdip** · 02-25-2020, 11:02 AM

Quote:

Originally Posted by weq92f

.
Be sure to put in the right amount of oil. Your compressor may have come with some oil already loaded but your system may call for more.

-klb

According to the compressor mfg. it comes with 220 cc's of oil, none required to be added.

**Sheepdip** · 02-25-2020, 11:04 AM

Quote:

Originally Posted by Kudzupatch

How much freon have you put in? You didn't say It is normal for it cycle when low and sounds to me from what you have posted you simply don't have enough refrigerant in the system yet.

24 oz's or 2 cans so far, that should be enough to at least move thru the compressor.

**Steeveedee** · 02-25-2020, 11:36 AM

Are you using the A6 or R4 compressor? BTW, you do not need to pull a vacuum on both ports, just the low side. Also, as a safety precaution, do not charge through the high side port.

**Sheepdip** · 02-25-2020, 06:43 PM

Quote:

Originally Posted by Steeveedee

Are you using the A6 or R4 compressor? BTW, you do not need to pull a vacuum on both ports, just the low side. Also, as a safety precaution, do not charge through the high side port.

It's an Old Air Products 21-2201SH which I believe is Sanden. It bolts right into the original GM brackets and the original hose manifold mates right to it.

RustyPile · 02-26-2020, 12:06 AM

It sounds like you have a blockage somewhere between the low pressure service port and the compressor.. This prevents the freon from reaching the compressor, hence, no head pressure or hi-side pressure until you pumped Freon (bad idea) into the hi-side.. I suspect you have a bad "upgraded" POA valve..

Unless you're looking for that original look, I'd get rid of the POA valve, condenser mounted drier, and expansion valve.. Get the appropriate parts, pieces, and hoses, and install a modern style system that cycles the compressor to maintain evaporator pressure/temperature..

**Sheepdip** · 02-26-2020, 10:42 AM

I spoke with a "Service Tech" at Old Air Products yesterday he said he believed my expansion valve was plugged or stuck shut, now with everything and I do mean everything brand new, I seriously doubted it was plugged.

I pulled the txv and it was wide open, I then put the bulb in ice water for 15 min. and it remained open, I then stuck the whole shebang in the freezer for 30 min. and it was closed when I removed it, then while blowing into it and putting the bulb in my warm hand it opened almost instantly.

This tells me it was not plugged and functioning as designed. I then reinstalled it.

I pulled a vacuum on the system and it held for a good 45 min with no drop. With the engine off I then filled thru the high side port, first can emptied within seconds high side came up to about 50psi, second took a little longer but I got it all in and high side read 90psi. I then closed my high side gauge and opened my low side gauge and it's at 90psi, the high and low had equalized with no cross feeding thru the gauge manifold. My compressor binary switch won't even let it come on at that pressure.

I bled thru the system low side port and took it down to about 40 psi, again cross checking pressures the high side came down to 40 psi also without opening the high side port. This tells me the 2 sides are equalizing some how.

I then started the engine/compressor, both sides remained at 40 psi, no change at higher rpm's either, I then started feeding gas thru the low side port (high side closed) and took the low side psi to about 50, cross checking.the high side also rose (equalized) to 50psi also and remained at 50.

I have installed 4 Auto A/C systems from scratch over the years with flawless results (all still working) this does not make me an expert by any means and I know there are people who are way smarter than I on A/C systems, but I'd bet a weeks pay my brand new compressor is not working as it's supposed to.

**Sheepdip** · 02-26-2020, 10:50 AM

Quote:

Originally Posted by RustyPile

It sounds like you have a blockage somewhere between the low pressure service port and the compressor.. This prevents the freon from reaching the compressor, hence, no head pressure or hi-side pressure until you pumped Freon (bad idea) into the hi-side.. I suspect you have a bad "upgraded" POA valve..

Unless you're looking for that original look, I'd get rid of the POA valve, condenser mounted drier, and expansion valve.. Get the appropriate parts, pieces, and hoses, and install a modern style system that cycles the compressor to maintain evaporator pressure/temperature..

I had wondered if possibly the POA upgrade could be the culprit since everything else was as it came from the factory. I will try and research exactly how those upgraded POA's work then go from there.

Andy4639 · 02-26-2020, 12:22 PM

I did this system 20 some years ago and it's still working great. Take the POA crap out altogether and buy accumulator and put the orifice tube in the connection under the battery in the line. This AC runs 36* on low in 90* outside temps all day with the upgraded compressor. I couldn't keep the old A-6 working with it cycling on/off. Everything bolted right up.

Andy4639 · 02-26-2020, 02:20 PM

Take the old A-6 out and install the kit I posted plus the late model 80's accumulator with orifice tube.

Andy4639 · 02-26-2020, 06:38 PM

Here is the setup now with 6.0 LS in. Had to get new compressor bracket to work with the LS swap. Everything else is the same.

Andy4639 · 02-26-2020, 08:05 PM

Couple more suggestions. These are ones I know work because they are on my 71 C-10 and 64 SS Impala.

C-10:
Take the cowl flapper out and seal off. Take the vacuum kick panel part off on the passenger side and install just the manual. Leave it open all the time. This will recirculate the cab air and it will be nice and cold. It was worth 5* on my 71 cab.
Both:
Take and put a manual hot water shut off in the hose opposite of the vacuum shut off. This will insure you have no hot water inside the vehicle.
Block off all air going around the radiator forcing it through the radiator for max cooling.
Both:
Make sure your motor driven are electric fans can handle the system you have installed.

**Sheepdip** · 02-27-2020, 06:27 PM

Got a second opinion yesterday from a reputable Auto A/C tech....new compressor on the way.

**Sheepdip** · 02-27-2020, 06:36 PM

Want to Thank Everyone for their input and suggestions to upgrade the whole enchilada, but I am staying with the basic old factory system sans the POA, R12 and Old Air Products aluminum bodied A6 compressor upgrade...it's only a retirees work truck, I can live with it's (by todays standards) short comings.

02-25-2020, 12:09 AM	#1
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,377	A/C Trouble Shooting Help Ok I'm looking for some suggestions on what's happening here with my A/C system. I'm leaning towards a bad compressor but I will be taking it to a pro for a second opinion before I cry wolf to the vendor if I can't resolve the issue with some guidance/suggestions from all you smart guy's out there. History: 1970 GMC... Everything is new, compressor, hoses, condenser, dryer/filter, POA upgrade valve with binary cut out switch, evaporator, expansion valve. With the exception of the POA upgrade valve all sourced thru LMC Truck. Today I pulled a vacuum on the new system, pulled right down both sides and held for over an hour with no issues. Here's where things went south, I started feeding the R134A into the suction side and it went to about 30 psi and climbing right away to about 50 psi and the binary switch kept cycling the clutch out ...high pressure side was almost nothing and remained almost nothing eventually climbing to about 25psi I then with the engine off I fed some refrigerant thru the high side port and got it up to about 100 psi then shut it down and went back to feeding thru the low port with the compressor engaged, I jumped the binary switch to keep the compressor from cycling in and out and got the low side up to about 70 psi, but I'm assuming all was from can pressure, because my high side is still 100 and never went any higher. I let it set for about an hour while I scratched my head and tried to figure it out. Rechecked the gauges and still 70psi on the low and 100psi on the high. It's like the compressor is not processing anything thru it. I'm open to suggestions if you got any.

02-25-2020, 08:17 AM	#2
A1971Blazer Senior Member Join Date: Nov 2013 Location: East Tennessee Posts: 2,107	Re: A/C Trouble Shooting Help member F.A.A.benny is the AC guru haven't seen posts from him in a while though __________________ 1967 C10 Step side 1968 C10 Step side 1970 Chevrolet K/5 Blazer 1972 Chevrolet K/5 Blazer .............

02-25-2020, 09:16 AM	#3
Kudzupatch Registered User Join Date: Apr 2013 Location: GUNTERSVILLE Posts: 621	Re: A/C Trouble Shooting Help How much freon have you put in? You didn't say It is normal for it cycle when low and sounds to me from what you have posted you simply don't have enough refrigerant in the system yet.

02-25-2020, 10:28 AM	#4
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 2,879	Re: A/C Trouble Shooting Help . Be sure to put in the right amount of oil. Your compressor may have come with some oil already loaded but your system may call for more. -klb __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

02-25-2020, 11:36 AM	#7
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,088	Re: A/C Trouble Shooting Help Are you using the A6 or R4 compressor? BTW, you do not need to pull a vacuum on both ports, just the low side. Also, as a safety precaution, do not charge through the high side port. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

02-26-2020, 12:06 AM	#9
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 1,531	Re: A/C Trouble Shooting Help It sounds like you have a blockage somewhere between the low pressure service port and the compressor.. This prevents the freon from reaching the compressor, hence, no head pressure or hi-side pressure until you pumped Freon (bad idea) into the hi-side.. I suspect you have a bad "upgraded" POA valve.. Unless you're looking for that original look, I'd get rid of the POA valve, condenser mounted drier, and expansion valve.. Get the appropriate parts, pieces, and hoses, and install a modern style system that cycles the compressor to maintain evaporator pressure/temperature..

02-26-2020, 10:42 AM	#10
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,377	Re: A/C Trouble Shooting Help I spoke with a "Service Tech" at Old Air Products yesterday he said he believed my expansion valve was plugged or stuck shut, now with everything and I do mean everything brand new, I seriously doubted it was plugged. I pulled the txv and it was wide open, I then put the bulb in ice water for 15 min. and it remained open, I then stuck the whole shebang in the freezer for 30 min. and it was closed when I removed it, then while blowing into it and putting the bulb in my warm hand it opened almost instantly. This tells me it was not plugged and functioning as designed. I then reinstalled it. I pulled a vacuum on the system and it held for a good 45 min with no drop. With the engine off I then filled thru the high side port, first can emptied within seconds high side came up to about 50psi, second took a little longer but I got it all in and high side read 90psi. I then closed my high side gauge and opened my low side gauge and it's at 90psi, the high and low had equalized with no cross feeding thru the gauge manifold. My compressor binary switch won't even let it come on at that pressure. I bled thru the system low side port and took it down to about 40 psi, again cross checking pressures the high side came down to 40 psi also without opening the high side port. This tells me the 2 sides are equalizing some how. I then started the engine/compressor, both sides remained at 40 psi, no change at higher rpm's either, I then started feeding gas thru the low side port (high side closed) and took the low side psi to about 50, cross checking.the high side also rose (equalized) to 50psi also and remained at 50. I have installed 4 Auto A/C systems from scratch over the years with flawless results (all still working) this does not make me an expert by any means and I know there are people who are way smarter than I on A/C systems, but I'd bet a weeks pay my brand new compressor is not working as it's supposed to.

02-26-2020, 12:22 PM	#12
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: A/C Trouble Shooting Help I did this system 20 some years ago and it's still working great. Take the POA crap out altogether and buy accumulator and put the orifice tube in the connection under the battery in the line. This AC runs 36* on low in 90* outside temps all day with the upgraded compressor. I couldn't keep the old A-6 working with it cycling on/off. Everything bolted right up. Attached Images __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

02-26-2020, 02:20 PM	#13
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: A/C Trouble Shooting Help Take the old A-6 out and install the kit I posted plus the late model 80's accumulator with orifice tube. Attached Images __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

02-26-2020, 06:38 PM	#14
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: A/C Trouble Shooting Help Here is the setup now with 6.0 LS in. Had to get new compressor bracket to work with the LS swap. Everything else is the same. Attached Images __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. Last edited by Andy4639; 02-26-2020 at 07:53 PM.

02-26-2020, 08:05 PM	#15
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: A/C Trouble Shooting Help Couple more suggestions. These are ones I know work because they are on my 71 C-10 and 64 SS Impala. C-10: Take the cowl flapper out and seal off. Take the vacuum kick panel part off on the passenger side and install just the manual. Leave it open all the time. This will recirculate the cab air and it will be nice and cold. It was worth 5* on my 71 cab. Both: Take and put a manual hot water shut off in the hose opposite of the vacuum shut off. This will insure you have no hot water inside the vehicle. Block off all air going around the radiator forcing it through the radiator for max cooling. Both: Make sure your motor driven are electric fans can handle the system you have installed. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

02-27-2020, 06:27 PM	#16
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,377	Re: A/C Trouble Shooting Help Got a second opinion yesterday from a reputable Auto A/C tech....new compressor on the way.

02-27-2020, 06:36 PM	#17
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,377	Re: A/C Trouble Shooting Help Want to Thank Everyone for their input and suggestions to upgrade the whole enchilada, but I am staying with the basic old factory system sans the POA, R12 and Old Air Products aluminum bodied A6 compressor upgrade...it's only a retirees work truck, I can live with it's (by todays standards) short comings.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.