Clogged Condensate Drain on 1978 C10 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

clockdoc · 07-30-2016, 05:14 PM

Hello folks. I recently got the AC on my '78 C10 Custom Deluxe working (was dead when I bought the truck in February). It's cooling well but today, in a heavy rain, I noticed what I thought was rainwater leaking onto the passenger-side floor. During a second trip later in the day, and after the rain had stopped and the floor had dried, I saw the same thing happening. I'm thinking that the condensate drain is clogged, allowing the water to rise high enough in the evaporator box to overflow and leak into the cab.

Now my problem is finding the drain to open it up! I was naively expecting to find a hose exiting the lower extremities of the box, and had visions of a shot of compressed air clearing it. I have yet to find it.

Any help will be greatly appreciated.

Clockdoc

**hatzie** · 07-30-2016, 05:40 PM

I believe there's not a hose. It's a huge floppy piece of rubber on the bottom of the evaporator box.
http://www.classicindustries.com/pro...ts/ap5002.html

clockdoc · 07-30-2016, 05:46 PM

Thanks Hatzie. Where is it located?

clockdoc · 07-30-2016, 06:36 PM

Sorry Hatzie! My question was a stupid one! You said on the bottom of the box. I have felt all around the bottom as far as I can reach and can't feel anything like that. Would you think that, if I drill (very carefully and with a pin vise) a small hole in the box so that I could apply a little air pressure,, I might be able to clear the blockage?

Clockdoc

**hatzie** · 07-30-2016, 06:42 PM

It should be right on the seam. There may only be a little slot.
When I pulled my 1976 AC box off the firewall I found a bunch of leaves and dirt in the bottom.

clockdoc · 07-30-2016, 06:58 PM

Thanks. I'll look again.

clockdoc · 07-31-2016, 04:59 PM

Finally found a picture of the bottom of the evaporator box (Attached). I've added a note to the pic to hilite the drain. It is a 3/8 to 1/2 inch hole--no tube--no flap, and it is very difficult to get a hand on. Was able to access it from beneath with a right-angle pick. When I did, I got a face full of water! All is well now.

Clockdoc

**hatzie** · 07-31-2016, 05:54 PM

There you go. They apparently improved it from 76. My 76 had a dirt and leaf filled 3/4" long 1-2 mm wide slot between the halves. I was tempted to drill a 3/8" hole.

clockdoc · 07-31-2016, 06:03 PM

Thanks for your help Hatzie

07-30-2016, 05:14 PM	#1
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Clogged Condensate Drain on 1978 C10 Hello folks. I recently got the AC on my '78 C10 Custom Deluxe working (was dead when I bought the truck in February). It's cooling well but today, in a heavy rain, I noticed what I thought was rainwater leaking onto the passenger-side floor. During a second trip later in the day, and after the rain had stopped and the floor had dried, I saw the same thing happening. I'm thinking that the condensate drain is clogged, allowing the water to rise high enough in the evaporator box to overflow and leak into the cab. Now my problem is finding the drain to open it up! I was naively expecting to find a hose exiting the lower extremities of the box, and had visions of a shot of compressed air clearing it. I have yet to find it. Any help will be greatly appreciated. Clockdoc

07-30-2016, 05:40 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,915	Re: Clogged Condensate Drain on 1978 C10 I believe there's not a hose. It's a huge floppy piece of rubber on the bottom of the evaporator box. http://www.classicindustries.com/pro...ts/ap5002.html __________________ 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.

07-30-2016, 05:46 PM	#3
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Clogged Condensate Drain on 1978 C10 Thanks Hatzie. Where is it located?

07-30-2016, 06:36 PM	#4
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Clogged Condensate Drain on 1978 C10 Sorry Hatzie! My question was a stupid one! You said on the bottom of the box. I have felt all around the bottom as far as I can reach and can't feel anything like that. Would you think that, if I drill (very carefully and with a pin vise) a small hole in the box so that I could apply a little air pressure,, I might be able to clear the blockage? Clockdoc

07-30-2016, 06:42 PM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,915	Re: Clogged Condensate Drain on 1978 C10 It should be right on the seam. There may only be a little slot. When I pulled my 1976 AC box off the firewall I found a bunch of leaves and dirt in the bottom. __________________ 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.

07-30-2016, 06:58 PM	#6
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Clogged Condensate Drain on 1978 C10 Thanks. I'll look again.

07-31-2016, 04:59 PM	#7
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Clogged Condensate Drain on 1978 C10 Finally found a picture of the bottom of the evaporator box (Attached). I've added a note to the pic to hilite the drain. It is a 3/8 to 1/2 inch hole--no tube--no flap, and it is very difficult to get a hand on. Was able to access it from beneath with a right-angle pick. When I did, I got a face full of water! All is well now. Clockdoc Attached Images

07-31-2016, 05:54 PM	#8
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,915	Re: Clogged Condensate Drain on 1978 C10 There you go. They apparently improved it from 76. My 76 had a dirt and leaf filled 3/4" long 1-2 mm wide slot between the halves. I was tempted to drill a 3/8" hole. __________________ 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.

07-31-2016, 06:03 PM	#9
clockdoc Registered User Join Date: Feb 2016 Location: Glen Allen, VA Posts: 67	Re: Clogged Condensate Drain on 1978 C10 Thanks for your help Hatzie



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