Head seems low on 98 GMC

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Mr Bill
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Joined: Sat Apr 30, 2016 8:17 am

Head seems low on 98 GMC

Postby Mr Bill » Thu Sep 08, 2016 3:32 pm

System cools ok, but I have seen a decline in vent temps over the past summer. It has the HT6, the suction is around 40 and the head around 180 which seems to low to me, can something happen inside these compressors to where they don't pump correctly? I've recovered the charge, pulled a good vacuum in the past month and weighed in the charge, no change, same vent temps, and same pressures. The compressor is about 10 years old, but it been good up to now, can they just wear out over a period of time. I'm a residential and commercial a/c tech, so I have a clue, but I'm lost on this. :mrgreen:

Joined: Sat Apr 30, 2016? Wow! we must have lost our original Joined date due to the upgrade. :mrgreen:
“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-
GM Tech
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Re: Head seems low on 98 GMC

Postby GM Tech » Thu Sep 08, 2016 4:29 pm

Does compressor turn very easily, like with one finger? Are there little "catches" as you rotate cmpressor? Are there stainless steel chips in the orifce tube? If all are true- the your compressor has imploded suction reeds on one or more pistons.. and is trashed....just one way to recognize- reed issues were usually in prior models- not so much in recent units...
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Mr Bill
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Re: Head seems low on 98 GMC

Postby Mr Bill » Thu Sep 08, 2016 4:45 pm

GM Tech wrote:Does compressor turn very easily, like with one finger? Are there little "catches" as you rotate cmpressor? Are there stainless steel chips in the orifce tube? If all are true- the your compressor has imploded suction reeds on one or more pistons.. and is trashed....just one way to recognize- reed issues were usually in prior models- not so much in recent units...


You know I didn't even try turning it, I guess it would be easy enough to just take the serpentine belt off and see, orifice is clean. Yeah I'm thinking the same thing, something inside messed up, never heard the term " imploded suction reeds" but I did check out a YouTube video of an exploded view of one, If I remember correctly, it had like 6 pistons. You can see the system equalizing really nice on the gauges when you turn the truck off, so my guess if something was stopped up, it probably would not equalize good. My gut all along was something was wrong inside the pump, it still blows out 52-54 going down the road @60 but it should be colder than that. Thanks for your feedback.
“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-
mk378
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Joined: Tue May 24, 2016 5:53 am

Re: Head seems low on 98 GMC

Postby mk378 » Thu Sep 08, 2016 5:20 pm

You don't have to remove serpentine belt, just turn the clutch plate by hand.

When there is a blown suction reed, that cylinder would not pump, but the discharge reed will still be there to keep refrigerant from flowing backwards through it. You'll end up with a compressor that still sort of works, but with less displacement.

Most home sized HVAC compressors are single cylinder, a single bad reed makes them fully dead.
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Mr Bill
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Re: Head seems low on 98 GMC

Postby Mr Bill » Fri Sep 09, 2016 6:56 am

Thanks for everyone's help, stuck a new pump on last night "when it was below 90°in Houston" and all seems well now, at idle I'm getting about 47°vent temps, I can live with that. Learn something new here about the reed valves. In my business, most every mfg. has gone to the scroll compressors, they seem to be bullet proof, I'm guess since my truck was built in 98 that the auto makers have gone to better and more efficient a/c compressors to. I choose to keep my 98 GMC because it's so easy to work on and is in great shape, and the compressor is right up on top of the engine. Although I'll probably never retire, "can't afford to" and coming up on 65 I just like the old school vehicles, they just seem a lot simpler, I like simple. :mrgreen:
“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-
DanielJohnson
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Joined: Sat Mar 04, 2017 12:38 am

Re: Head seems low on 98 GMC

Postby DanielJohnson » Sat Mar 04, 2017 12:44 am

Gained much information.
DarrylS
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Re: Head seems low on 98 GMC

Postby DarrylS » Sat Apr 15, 2017 4:52 am

I had a few of those old HT6's and clutch's in my workshop but threw them all out after the great flood of 2010. You used to be able to get a kit and completely rebuild them fairly easily. Did probably a dozen or so back years ago was kind of a hobby LOL

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