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Help with '93 K1500 A/C

Fossil_Fuel on Thu September 24, 2015 11:34 PM User is offline

Year: 1993
Make: Chev
Model: K1500 pickup
Engine Size: 5.7
Refrigerant Type: R134
Ambient Temp: 70 F
Pressure Low: 125
Pressure High: 130
Country of Origin: United States

Truck is new to me. A/c looks unmolested.

Static pressures are about 70 psi

Compressor engages and stays engaged but does cycle after running for some time

Suction lines are cold and are frosting up

High side line into condenser is warm
Exit line from condenser is cold

Immediately pegs the low side at 125 when turned on
High side reads about the same 130-140

What is the next step to determine what is wrong?

I do not know how much charge is in the system but the low side does not pull down in pressure at all. It goes up right away.

Any help/suggestions would be appreciated.

Thanks




Dougflas on Fri September 25, 2015 1:34 AM User is offline

Just a few quick questions. If I remember correctly, there was a control head wire modification way back then for GM pick up trucks. I think it had to do with a green wire out of the control head. On your problem, where is the orfice tube located? Is it at the condenser or directly at the evaporator? Is the blower motor running?

GM Tech on Fri September 25, 2015 3:55 AM User is offline

Your low side pressure reading is bad- or you have your valves open at your manifold- make sure you have the hoses on your conversion port adapters properly.

1993 was last year for R-12 on a C/K truck.

Frosting back to compressor would be low pressure (in the 20's).

Cold from condenser outlet is normal on a C/K Truck, since orifice tube is in condenser outlet pipe.

Number one cause of a/c issues is loss of refrigerant- the only way to know is to extract and weigh current charge. Has this been done lately? Has it been recharged to 80% of R-12 Specification?

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cussboy on Fri September 25, 2015 8:41 AM User is offline

If it's an R4 compressor: I had issues with those in my 1988 and 1994 Suburbans, never had one last more than 3 years. But those also had dual AC.

GM Tech on Fri September 25, 2015 9:10 AM User is offline

Control head issue was 91 thru 92 MY BTW not hard to remember- I lived it..... Belt jumping was '93's big issue-- would tear the terminals off the R-4 coil...

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Fri September 25, 2015 at 9:11 AM by GM Tech

mk378 on Fri September 25, 2015 11:24 AM User is offline

When you have frost on the accumulator, refrigeration is working well. The air should be cold. The usual problem when it is not is that the air door under the dash is not blocking off the heater when you set the controls for full cold, so the air coming to the vents has been reheated.

If cycling switch is stuck closed, the air will get cold at first but then warm again because the evaporator has frosted up. Compressor should cycle off at about 25 psi low side. If it does not, unplug switch (on accumulator) and compressor should stop, confirming the wiring is OK. You can R&R switch with the system charged.

Edited: Fri September 25, 2015 at 11:25 AM by mk378

Fossil_Fuel on Fri September 25, 2015 8:58 PM User is offline

Thanks for the replies and help.
GM Tech was spot on !!


1). I did have the gage manifold valves open.... Duh! Thanks for pointing that out.

2) 93 was last year for R12. I did not know exactly which year was the last so thanks. I listed R134 because it has the correct couplers and the compressor has a r134 listed on it. After more detailed look it seems that this was retrofitted with 134. Has adapters on the connections and it must have had the compressor changed. Sticker on the accumulator still has R12 sticker on it.


Well after I connected the Gages (and shut the valves) it is just as expected. Low pressures . 22 and 130.
I charged the system up to 33 and 150 and all is good. Took about 10 oz. Schrader on high side has slow leak so I will probably need to adress that next spring.

Thanks again guys.



Edited: Fri September 25, 2015 at 9:06 PM by Fossil_Fuel

mk378 on Fri September 25, 2015 9:30 PM User is offline

You should have cycling at 70 ambient, especially if you rev the engine (1500-2000 rpm). If your low side is going below 20 with the compressor still on, there will be freeze-up problems.

Edited: Fri September 25, 2015 at 9:34 PM by mk378

Fossil_Fuel on Fri September 25, 2015 9:43 PM User is offline

It was only 59 deg F when I charged the system. I will recheck at higher ambient temp if it gets above 70 again this fall !

Cussboy on Sat September 26, 2015 9:22 AM User is offline

Yes, 1993 was last year for R-12 with these; my 1994 Suburban was factory R134a, still used the r4.


Quote
Originally posted by: Fossil_Fuel
It was only 59 deg F when I charged the system. I will recheck at higher ambient temp if it gets above 70 again this fall !


Ha ! Here in Phoenix it will be about 105F today !

ice-n-tropics on Sun October 11, 2015 9:45 PM User is offline

Hi GM Tech
Remember the field countermeasure for throwing R-4 belts in 93 MY?
Added tension braces to dampen the vibs and change the natural frequency.
I toured the HRD compressor factory in Dayton and a team of union employees gave a presentation
HRD gave A/C training to these guys and they gave the tour
Surprisingly the main spokesman was very A/C knowledgeable. Was that guy "GM Tech"?
hotrodac


-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

GM Tech on Sun October 11, 2015 10:24 PM User is offline

I was there-have done numerous presentations- can't remember that specific group-- but the reason the belts were thrown was due to slugging the compressor due to siphoning through the accumulator and preloading the compressor full of liquid refrigerant. I had a see-thru A/d and a see-through front head on an R-4 compressor to prove what was going on. Seems the A/D tubing process was improved by roll forming the inner tube to the outer cup- a perfect seal with roll form instead of expaned form. Now with that improvement the a/d tube could now form a siphon (no gas leak at the new roll formed commection)- the ultimate answer to belt jumping was to put an anti-siphon hole in the top of the tube (at the roll form) to bust up the siphon ability. Besides, this is what Ford had done for years- is what I showed the Truck group at the GM tech center in Warren Mi- The next year the anti siphon hole became known as the pressure equalization hole (on the print) and was implemented on all A/ds. Belt jumping stopped 100% . Heck we had well over 1000 cases returned to us in
warranty in early 93 model year

There was also a difference in belts/belt material- I was able to easily duplicate belt jumping based on compressor slugging and video taped (slow mrtion) belt material "A" jumping forward of of idler (not tensioner) where it simply dropped below the idler pulley and all systems are go- just that belts runs freely below the pulley and looks like no one had ever wrapped the idler pulley. Belt material "B" would jump off the idler but rearward, where it got caught behind the idler axle and force the belt to come off the compressor pulley and tear up the coil terminals and create a "walk-home".

Any field countermeasures created then were just in hopes of stopping what was never duplicated- all theory related-as a matter of fact this is the first time I have ever heard of the braces (other than for noise abatement)- I had the videos and the exact answer, and a 93 truck in my lab, and was to exactly re-create the failure mode and be satisified we stopped the issue for the next model year.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

GM Tech on Sun October 11, 2015 10:24 PM User is offline

I was there-have done numerous presentations- can't remember that specific group-- but the reason the belts were thrown was due to slugging the compressor due to siphoning through the accumulator and preloading the compressor full of liquid refrigerant. I had a see-thru A/d and a see-through front head on an R-4 compressor to prove what was going on. Seems the A/D tubing process was improved by roll forming the inner tube to the outer cup- a perfect seal with roll form instead of expaned form. Now with that improvement the a/d tube could now form a siphon (no gas leak at the new roll formed commection)- the ultimate answer to belt jumping was to put an anti-siphon hole in the top of the tube (at the roll form) to bust up the siphon ability. Besides, this is what Ford had done for years- is what I showed the Truck group at the GM tech center in Warren Mi- The next year the anti siphon hole became known as the pressure equalization hole (on the print) and was implemented on all A/ds. Belt jumping stopped 100% . Heck we had well over 1000 cases returned to us in
warranty in early 93 model year

There was also a difference in belts/belt material- I was able to easily duplicate belt jumping based on compressor slugging and video taped (slow mrtion) belt material "A" jumping forward of of idler (not tensioner) where it simply dropped below the idler pulley and all systems are go- just that belts runs freely below the pulley and looks like no one had ever wrapped the idler pulley. Belt material "B" would jump off the idler but rearward, where it got caught behind the idler axle and force the belt to come off the compressor pulley and tear up the coil terminals and create a "walk-home".

Any field countermeasures created then were just in hopes of stopping what was never duplicated- all theory related-as a matter of fact this is the first time I have ever heard of the braces (other than for noise abatement)- I had the videos and the exact answer, and a 93 truck in my lab, and was to exactly re-create the failure mode and be satisified we stopped the issue for the next model year.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

ice-n-tropics on Tue October 13, 2015 10:00 AM User is offline

GM Tech, Thanks for reply.
Memory was a little fuzzy about tension braces field countermeasure. Your explanation reminded me that tension brace field countermeasure helped NVH only.
I was at HRD Dayton related to sharing at time HRD was planning scroll production sharing with Sanden and maybe met you at that time.
I,ve also done lots of slugging investigations with transparent Lexan or Plexiglas A/C components including AD, suction sight glasses etc.
I think Jay Amin at FoMoCo inovated the anti siphon hole.
Heck, I,ve seen up to 3 separate slugs (on Humvee) hit the compressor suction based on evap construction, suction hose droop and component elevations.
Interesting how slug has high oil content based on color
Refrigerant migrates and condenses a the coldest part of the static A/C system. This is a huge problem on Agricultural vehicles with a cab evap warming in the morning sun while the compressor is cold. Liquid refrigerant washes oil out of the crankcase over several non operating days and the comp seizes on startup. Denso on Deer had to add a accumulator on a TXV system as seizure countermeasure on some models
One of my one-off installations A/C with 2 banger had to use both slack and tight side idlers to prevent belt throw.
hotrodac
"How to Air Condition Your Hot Rod" book avaliable from Vintage Air




-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

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