73 ac rebuild, need guidance - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ky-donzi · 07-13-2022, 09:22 AM

I’m gathering parts and want to make sure I’m on the right track.

Background:
73 blazer basically I have no ac parts except the ductwork and Evap housing.

New parts ordered:
Evap
Accumulator
Line set
Pro6ten compressor
Binary hi/lo switch
134 blue orifice tube and adapter (to run in the larger Evap pipe from the early trucks)
Parallel flow condenser

The original schematic shows to engage the compressor clutch it has to be satisfied by low pressure switch and then in series by the thermal switch to pass current to the clutch coil.

So my main question is will I still wire my thermal coupling compressor cut out switch in series with the compressor clutch, or just use the hi/low binary switch for compressor cycling

Thanks

**hatzie** · 07-13-2022, 09:49 PM

The binary switch is a combination LPCO HPCO switch
Put the binary switch in the high side plumbing off the compressor and keep the original LPCO on the accumulator/dryer.

Run the thermal cutout switch in series with the other two.

I usually dump all the oil out of the new compressor and fill it with the same amount of fresh ester or PAG oil with UV dye and inject the rest of the oil charge once the system is vacuumed down.

I'm interested to read how well that A6 replacement works.

ky-donzi · 07-13-2022, 11:04 PM

Awesome,thanks!

Just to verify..... the thermal switch I’m referencing is the one that mount on the hvac box and probs into the Evap coil to monitor freeze up....not a superheat thermal cut out

Are we talking about the same switch?

Reid

**hatzie** · 07-14-2022, 10:03 AM

Yes. That thermal switch is there to cycle the compressor to keep the evaporator from icing up.
A fully charged system shouldn't have trouble with evaporator icing but early automotive AC systems leaked.

ky-donzi · 07-14-2022, 10:16 AM

Thanks!

I was confused for a little bit on the difference between a modern cycling switch and the binary switch.

Also I was confused about the low side of the binary switch ever doing anything since it was in the liquid line....but since talked to someone about it being more like a absolute low switch (basically completely out of refrigerant) to ever trip the low side.

I think I understand what’s going on now.....thanks again

07-13-2022, 09:22 AM	#1
ky-donzi Registered User Join Date: Jun 2012 Location: madisonville ky Posts: 310	73 ac rebuild, need guidance I’m gathering parts and want to make sure I’m on the right track. Background: 73 blazer basically I have no ac parts except the ductwork and Evap housing. New parts ordered: Evap Accumulator Line set Pro6ten compressor Binary hi/lo switch 134 blue orifice tube and adapter (to run in the larger Evap pipe from the early trucks) Parallel flow condenser The original schematic shows to engage the compressor clutch it has to be satisfied by low pressure switch and then in series by the thermal switch to pass current to the clutch coil. So my main question is will I still wire my thermal coupling compressor cut out switch in series with the compressor clutch, or just use the hi/low binary switch for compressor cycling Thanks __________________ 61 GMC 4x4 1-ton flatbed 4bt cummins, ranger od, sm465, np 205, d60F, d70R 4.11 10,000 ramsey PTO winch.... SOLD 73 k5 gm crate 350-265 / sm465 / np205 3.73 posi Last edited by ky-donzi; 07-13-2022 at 09:29 AM.

07-13-2022, 09:49 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,916	Re: 73 ac rebuild, need guidance The binary switch is a combination LPCO HPCO switch Put the binary switch in the high side plumbing off the compressor and keep the original LPCO on the accumulator/dryer. Run the thermal cutout switch in series with the other two. I usually dump all the oil out of the new compressor and fill it with the same amount of fresh ester or PAG oil with UV dye and inject the rest of the oil charge once the system is vacuumed down. I'm interested to read how well that A6 replacement works. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

07-13-2022, 11:04 PM	#3
ky-donzi Registered User Join Date: Jun 2012 Location: madisonville ky Posts: 310	Re: 73 ac rebuild, need guidance Awesome,thanks! Just to verify..... the thermal switch I’m referencing is the one that mount on the hvac box and probs into the Evap coil to monitor freeze up....not a superheat thermal cut out Are we talking about the same switch? Reid __________________ 61 GMC 4x4 1-ton flatbed 4bt cummins, ranger od, sm465, np 205, d60F, d70R 4.11 10,000 ramsey PTO winch.... SOLD 73 k5 gm crate 350-265 / sm465 / np205 3.73 posi

07-14-2022, 10:03 AM	#4
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,916	Re: 73 ac rebuild, need guidance Yes. That thermal switch is there to cycle the compressor to keep the evaporator from icing up. A fully charged system shouldn't have trouble with evaporator icing but early automotive AC systems leaked. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

07-14-2022, 10:16 AM	#5
ky-donzi Registered User Join Date: Jun 2012 Location: madisonville ky Posts: 310	Re: 73 ac rebuild, need guidance Thanks! I was confused for a little bit on the difference between a modern cycling switch and the binary switch. Also I was confused about the low side of the binary switch ever doing anything since it was in the liquid line....but since talked to someone about it being more like a absolute low switch (basically completely out of refrigerant) to ever trip the low side. I think I understand what’s going on now.....thanks again __________________ 61 GMC 4x4 1-ton flatbed 4bt cummins, ranger od, sm465, np 205, d60F, d70R 4.11 10,000 ramsey PTO winch.... SOLD 73 k5 gm crate 350-265 / sm465 / np205 3.73 posi



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