AC Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ADub · 07-21-2012, 07:14 PM

My recently purchased 71 burb has factory AC. Has the tunnel up to the front, no evaporator or vents in the dash. P/O had it converted to R134. Still has the old Frigidaire compressor, but they put new lines in it. Last time I drove it was 2 weeks ago, AC worked. Today it does not. AC blows, compressor kicks on, but the vents don't blow cold air. I don't have a gauge set, but I had a cheapy AC filler with gauge sitting in the garage, so I checked low side pressure. Its at 35 PSI with the compressor running. Compressor hot side gets very hot, but the compressor cold side does not get cold. I can see fluid moving in the sight glass fwiw.

Is the compressor toast?

AzDon · 07-21-2012, 09:47 PM

Impossible to diagnose the problem without complete info...... Need to put a pair of gauges on it to see the pressure differential. The high pressure side "sprays" liquid freon as a mist into the low pressure "evaporator coils". If the compressor is operating and pressures of 200-350 (high side) and 15-40 (low side) are showing, I would recommend replacing the accumulator tank and recharging the system with the appropriate amount of pag-150 and freon after a good vacuum-down.

ADub · 07-23-2012, 08:14 AM

I'll go rent a set of gauges this week and post up the details.

ADub · 07-26-2012, 06:13 PM

Engine idling

Low side 35 psi, high side 150psi

Engine at 1500rpm

Low side 12 psi, High side 160 psi

Engine off
85psi

Vent temps only dropped a couple degrees from ambient.

What do you think?

Street Smart · 07-26-2012, 10:35 PM

Pressures look low, especially on a hot day.
Does your reciever/dyer have a sight glass on it? If it does look for any bubbles, if so thats a sign of low freon.

ADub · 07-26-2012, 11:19 PM

It does. Can't see any bubbles, just looks like fluid flowing

ADub · 07-27-2012, 08:39 PM

I added some freon and brought the pressures up to 35 low 250 high. Didnt really change anything, vent temps were in the mid 80s

Street Smart · 07-28-2012, 05:27 AM

Check that the blend door moves when you go from hot to cold on the dash. Also pinch off the heater hose coming from the intake (this will check that the heater control valve is letting hot coolant in).

Street Smart · 07-28-2012, 05:28 AM

Feel the AC hoses under the hood, anything cold or sweating?

ADub · 07-28-2012, 07:16 AM

Rear ac only, there is no blend door. As for hoses, one is cooler than the other but it doesn't get cold and sweat
Posted via Mobile Device

07-21-2012, 07:14 PM	#1
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	AC Help My recently purchased 71 burb has factory AC. Has the tunnel up to the front, no evaporator or vents in the dash. P/O had it converted to R134. Still has the old Frigidaire compressor, but they put new lines in it. Last time I drove it was 2 weeks ago, AC worked. Today it does not. AC blows, compressor kicks on, but the vents don't blow cold air. I don't have a gauge set, but I had a cheapy AC filler with gauge sitting in the garage, so I checked low side pressure. Its at 35 PSI with the compressor running. Compressor hot side gets very hot, but the compressor cold side does not get cold. I can see fluid moving in the sight glass fwiw. Is the compressor toast? __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd

07-21-2012, 09:47 PM	#2
AzDon Registered User Join Date: Oct 2008 Location: Lake Havasu,AZ Posts: 202	Re: AC Help Impossible to diagnose the problem without complete info...... Need to put a pair of gauges on it to see the pressure differential. The high pressure side "sprays" liquid freon as a mist into the low pressure "evaporator coils". If the compressor is operating and pressures of 200-350 (high side) and 15-40 (low side) are showing, I would recommend replacing the accumulator tank and recharging the system with the appropriate amount of pag-150 and freon after a good vacuum-down.

07-23-2012, 08:14 AM	#3
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	Re: AC Help I'll go rent a set of gauges this week and post up the details. __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd

07-26-2012, 06:13 PM	#4
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	Re: AC Help Engine idling Low side 35 psi, high side 150psi Engine at 1500rpm Low side 12 psi, High side 160 psi Engine off 85psi Vent temps only dropped a couple degrees from ambient. What do you think? __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd

07-26-2012, 10:35 PM	#5
Street Smart Registered User Join Date: Dec 2009 Location: Brooklyn N.Y. Posts: 819	Re: AC Help Pressures look low, especially on a hot day. Does your reciever/dyer have a sight glass on it? If it does look for any bubbles, if so thats a sign of low freon. __________________ 1967 GMC Suburban, Supercharged 6.2 LS with a 6l80e , my 11 second tow vehicle! pic in my profile 1987 GMC CrewCab Dually 6.0 LS/6L90e, new tow pig. http://67-72chevytrucks.com/gallery/...=74049&cat=500

07-26-2012, 11:19 PM	#6
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	Re: AC Help It does. Can't see any bubbles, just looks like fluid flowing __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd

07-27-2012, 08:39 PM	#7
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	Re: AC Help I added some freon and brought the pressures up to 35 low 250 high. Didnt really change anything, vent temps were in the mid 80s __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd

07-28-2012, 05:27 AM	#8
Street Smart Registered User Join Date: Dec 2009 Location: Brooklyn N.Y. Posts: 819	Re: AC Help Check that the blend door moves when you go from hot to cold on the dash. Also pinch off the heater hose coming from the intake (this will check that the heater control valve is letting hot coolant in). __________________ 1967 GMC Suburban, Supercharged 6.2 LS with a 6l80e , my 11 second tow vehicle! pic in my profile 1987 GMC CrewCab Dually 6.0 LS/6L90e, new tow pig. http://67-72chevytrucks.com/gallery/...=74049&cat=500

07-28-2012, 05:28 AM	#9
Street Smart Registered User Join Date: Dec 2009 Location: Brooklyn N.Y. Posts: 819	Re: AC Help Feel the AC hoses under the hood, anything cold or sweating? __________________ 1967 GMC Suburban, Supercharged 6.2 LS with a 6l80e , my 11 second tow vehicle! pic in my profile 1987 GMC CrewCab Dually 6.0 LS/6L90e, new tow pig. http://67-72chevytrucks.com/gallery/...=74049&cat=500

07-28-2012, 07:16 AM	#10
ADub Registered User Join Date: Dec 2010 Location: Houston, TX Posts: 218	Re: AC Help Rear ac only, there is no blend door. As for hoses, one is cooler than the other but it doesn't get cold and sweat Posted via Mobile Device __________________ 69 C10 SWB LY6 T56 70 Chevelle SS 396 4spd



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