A/C System Trouble Shooting

[Sheepdip]

Ok I'm looking for some suggestions on what's happening here with my A/C system.

I'm leaning towards a bad compressor but I will be taking it to a pro for a second opinion before I cry wolf to the vendor if I can't resolve the issue with some guidance/suggestions from all you smart guy's out there.

History: 1970 GMC... Everything is new, compressor, hoses, condenser, dryer/filter, POA upgrade valve with binary cut out switch, evaporator, expansion valve.

With the exception of the POA upgrade valve all sourced thru LMC Truck.

Today I pulled a vacuum on the new system, pulled right down both sides and held for over an hour with no issues.
Here's where things went south, I started feeding the R134A into the suction side and it went to about 30 psi and climbing right away to about 50 psi and the binary switch kept cycling the clutch out ...high pressure side was almost nothing and remained almost nothing eventually climbing to about 25psi

I then with the engine off I fed some refrigerant thru the high side port and got it up to about 100 psi then shut it down and went back to feeding thru the low port with the compressor engaged, I jumped the binary switch to keep the compressor from cycling in and out and got the low side up to about 70 psi, but I'm assuming all was from can pressure, because my high side is still 100 and never went any higher.

I let it set for about an hour while I scratched my head and tried to figure it out. Rechecked the gauges and still 70psi on the low and 100psi on the high.

It's like the compressor is not processing anything thru it.

I'm open to suggestions if you got any.

[davischevy]

Do you have a sight glass on the dryer? Is refrigerant moving through it?

[randy500]

The POA upgrade is no upgrade at all, its pure junk. Garbage, a fix for something that isnt a problem, etc. not to mentioning the original truck system isn't designed for that downgrade orifice cycling system. Also the A6 compressor clutch isnt made for cycling on and off constantly.

People have made them work so now my rant is over and i will explain what to do.

Your best bet is to install a POA valve which is calibrated for r134a.

[davischevy]

I was trying to ease into it, but since Randy spoke the truth, I will chime in.

Randy is right. I have FAA Benny (board member) recalibrate my POA valves.

[randy500]

Tips on charging the system.

You don't charge by pressure. Ignore pressure until system is charged.

1. Evac your current charge and pull a vacuum.
2. Charge liquid (can inverted) into the vacuum on the high side with the engine off.
Purge charge line until liquid comes the fitting at the manifold.

Your charging into the high side to prevent liquid from hydrolocking the compressor

3. Charge by weight, if your using small cans weigh each can carefully before and after to calculate how much you installed, a digital postal scale works and is cheap. Write down all your weights and calculations, charge weight is very critical
4. Heat the cans with a hair dryer to push liquid and or vapor into the system.

You should be able to get almost all the charge in the system by heating the cans and liquid charging.

Start the engine and finish charging vapor into the low side.

Charge weight is very very critical

You cant tell how much refrigerant is in the system by pressures, you have to calculate it when charging.
You can look up refrigerant loss in hoses, it can be more than an ounce if liquid is in the hoses. Its part of your charge calculation, so factor in something for refrigerant still in hoses.

Example,
starting can weight with hose attached and inverted, write it down
Purge charging hose with liquid, what is the can weight now, write it down... difference in weight is amount in hoses.

[Richard]

Notice you said you installed the poa update and expansion valve. The "POA upgrade" typically comes with an orifice and expansion valve delete tube. The expansion valve is eliminated. The system will not work with two expansion devices. Most compressors are shipped dry, did you add oil? As said best to charge by weight. At least to get in the right ballpark. When converting to R134a 15% less than the R22 charge is a good starting point. A larger than stock or more efficient condenser is highly recommended if you want decent cooling at idle or low speeds. I had some success on one conversion using a stock condenser by installing auxiliary electric fans. The TXV type system will work great when properly installed and charged. The orifice tube systems were and are used as a cost cutting solution.

[Sheepdip]

Originally Posted by davischevy

Do you have a sight glass on the dryer? Is refrigerant moving through it?

Yes it has the sight glass but saw no movement or indication of refrigerant passing thru it.

[Sheepdip]

Originally Posted by davischevy

I was trying to ease into it, but since Randy spoke the truth, I will chime in.

Randy is right. I have FAA Benny (board member) recalibrate my POA valves.

From what I read trying to do my homework before the fact, is there are 2 mfgs. of POA valves Frigidaire and Delco, the Delco which I have is non rebuildable and is why I went to the upgrade kit

[Sheepdip]

Originally Posted by randy500

The POA upgrade is no upgrade at all, its pure junk. Garbage, a fix for something that isnt a problem, etc. not to mentioning the original truck system isn't designed for that downgrade orifice cycling system. Also the A6 compressor clutch isnt made for cycling on and off constantly.

People have made them work so now my rant is over and i will explain what to do.

Your best bet is to install a POA valve which is calibrated for r134a.

From what I read trying to do my homework before the fact, is there are 2 mfgs. of POA valves Frigidaire and Delco, the Delco which I have is non rebuildable and is why I went to the upgrade kit

[Sheepdip]

Originally Posted by Richard

Notice you said you installed the poa update and expansion valve. The "POA upgrade" typically comes with an orifice and expansion valve delete tube. The expansion valve is eliminated. The system will not work with two expansion devices. Most compressors are shipped dry, did you add oil? As said best to charge by weight. At least to get in the right ballpark. When converting to R134a 15% less than the R22 charge is a good starting point. A larger than stock or more efficient condenser is highly recommended if you want decent cooling at idle or low speeds. I had some success on one conversion using a stock condenser by installing auxiliary electric fans. The TXV type system will work great when properly installed and charged. The orifice tube systems were and are used as a cost cutting solution.

No expansion valve elimination tube was included, the old POA worked with an exp. valve. Some of the upgrade kits I looked at included a new exp. valve so that part confuses me I guess.

Compressor is a Sanden configured to bolt in to factory brackets and came pre-oiled with 220 cc's of oil.

The new condenser is larger than the factory original.

[Sheepdip]

Originally Posted by randy500

Tips on charging the system.

You don't charge by pressure. Ignore pressure until system is charged.

1. Evac your current charge and pull a vacuum.
2. Charge liquid (can inverted) into the vacuum on the high side with the engine off.
Purge charge line until liquid comes the fitting at the manifold.

Your charging into the high side to prevent liquid from hydrolocking the compressor

3. Charge by weight, if your using small cans weigh each can carefully before and after to calculate how much you installed, a digital postal scale works and is cheap. Write down all your weights and calculations, charge weight is very critical
4. Heat the cans with a hair dryer to push liquid and or vapor into the system.

You should be able to get almost all the charge in the system by heating the cans and liquid charging.

Start the engine and finish charging vapor into the low side.

Charge weight is very very critical

You cant tell how much refrigerant is in the system by pressures, you have to calculate it when charging.
You can look up refrigerant loss in hoses, it can be more than an ounce if liquid is in the hoses. Its part of your charge calculation, so factor in something for refrigerant still in hoses.

Example,
starting can weight with hose attached and inverted, write it down
Purge charging hose with liquid, what is the can weight now, write it down... difference in weight is amount in hoses.

I will give this a try this afternoon and see if it helps or improves my situation. Still puzzles me as to why my high side remains stagnant, seems like the compressor should process the low side of 70 psi into the high side reading drawing the low side down to a corrected differential if the compressor is working as it should. Next question is does anyone know how many pounds/ounces of 134a a stock 70 GMC system requires.

[Daaaanz67]

Here’s an adjustment I came across. Hope it comes up not to good at this.

[randy500]

If you dont have a sufficient charge you wont get high side pressure.
Pressure on the high side is created by compressing vapor state refrigerant into the high side before the expansion device, there is a lot of volume between the compressor and the expansion device and it takes a mostly full charge to be able to stack up refrigerant on the high side.

Stacked up refrigerant in a liquid state is what you see in the sight glass, if considerably undercharged, say a pound or so, you wont see much of anything in the sight glass.

[Sheepdip]

I spoke with a "Service Tech" at Old Air Products yesterday he said he believed my expansion valve was plugged or stuck shut, now with everything and I do mean everything brand new, I seriously doubted it was plugged.

I pulled the txv and it was wide open, I then put the bulb in ice water for 15 min. and it remained open, I then stuck the whole shebang in the freezer for 30 min. and it was closed when I removed it, then while blowing into it and putting the bulb in my warm hand it opened almost instantly.

This tells me it was not plugged and functioning as designed. I then reinstalled it.

I pulled a vacuum on the system and it held for a good 45 min with no drop. With the engine off I then filled thru the high side port, first can emptied within seconds high side came up to about 50psi, second took a little longer but I got it all in and high side read 90psi. I then closed my high side gauge and opened my low side gauge and it's at 90psi, the high and low had equalized with no cross feeding thru the gauge manifold. My compressor binary switch won't even let it come on at that pressure.

I bled thru the system low side port and took it down to about 40 psi, again cross checking pressures the high side came down to 40 psi also without opening the high side port. This tells me the 2 sides are equalizing some how.

I then started the engine/compressor, both sides remained at 40 psi, no change at higher rpm's either, I then started feeding gas thru the low side port (high side closed) and took the low side psi to about 50, cross checking.the high side also rose (equalized) to 50psi also and remained at 50.

I have installed 4 Auto A/C systems from scratch over the years with flawless results (all still working) this does not make me an expert by any means and I know there are people who are way smarter than I on A/C systems, but I'd bet a weeks pay my brand new compressor is not working as it's supposed to.

[Andy4639]

I don't claim to be expert here by any means but you stated...

With the engine off I then filled thru the high side port, first can emptied within seconds high side came up to about 50psi,

I have never put Freon in on the high side.

Also every compressor I have installed the directions state to hand turn them 20-30 times before and after you charge it.

[Sheepdip]

Originally Posted by Andy4639

I don't claim to be expert here by any means but you stated...



I have never put Freon in on the high side.

Also every compressor I have installed the directions state to hand turn them 20-30 times before and after you charge it.

Neither have I till yesterday, just trying what Randy suggested and that changed nothing.

[randy500]

To be clear....

Only charge the high side with engine off for initial fill. Fills much faster and prevents liquid building up in or near the compressor which can hydrolock it.

[Sheepdip]

Posted by Rustypile:
It sounds like you have a blockage somewhere between the low pressure service port and the compressor.. This prevents the freon from reaching the compressor, hence, no head pressure or hi-side pressure until you pumped Freon (bad idea) into the hi-side.. I suspect you have a bad "upgraded" POA valve..



Rusty...This is a very strong possibility that I will research today.

[randy500]

What is your charge weight goal? 3.5 * 80%? ...3.5 pound factory charge reduced to 80% for r134, 45oz, appox

You put in the majority of 2 12 oz cans? So you have maybe 22oz in there, Your way short on charge and wont make any pressure.

Fill the system while not running using a hair dryer on the cans to liquid charge the high side until full.

If there is essentially nothing to pump you wont get pressure. You can also Force the expansion valve closed by cooling it in ice to see of it builds pressure.

High and low side always equalize when not running. The sides are only separated by the compressor and the expansion device. Both do not completely seal.

[randy500]

What is your aversion to filling the system?

Seems like you are trying real hard to do a slow vapor charge into the low side with the pressure cutoff switches preventing the pump from running.

And are you even doing a charge by exact weight? R134 charge weight is very critical, you cant rely on the sight glass for charge indication like you can with r12. Even if you get pressure you probably wont have good cooling without knowing the charge weight.

[randy500]

Pressure is created by moving volume through a restriction.

Assuming the pump is pumping....(you have no evidence that it isnt and its new)
Do you have a volume problem (low charge)
Or
Open orifice, (is the expansion valve open because the bulb isnt insulated?) or some other reason,

If you close the orifice you should see some rise in high side pressure if the pump is pumping and you have sufficient volume of charge.
If you dont then the pump is not pumping.

[randy500]

Go ahead and listen to rustypile and Andy and whoever else posts about not charging into the high side....both are ignorant of AC systems.

The high side is only the high side when running.
The 2 sides are only separated by the expansion device and the pump and neither is completely sealed.

Pressure in the system high and low side is equal when at rest.
Pressure at rest is not dependent on charge volume.
Resting pressure is equal (in both sides) to the temp pressure charts of the refrigerant...vapor pressure.

[randy500]

I just thought of one more thing on your equalizing pressures....
Are you sure the low side shrader valve is opening?
Sometimes the hoses dont depress the valve all the way, just enough to move the gauge.

Testing:
With refrigerant can on scale,
Engine off.
Can inverted for liquid charge
Open the fill valve on your manifold, does the can weight change, and not just enough to fill the hoses?
Does heating the can move the refrigerant, scale weight significantly changes?

If no then the shrader valve is not open.

[Davidf]

I agree with others. If the high side is low, there are two causes: 1. Low refrigerant or 2. failed Compressor.

I would think that if there was a blockage in the system, the high side would be high.

The sight glass is worthless with R134a.

POA eliminators are junk or annoying at best. A constantly cycling compressor will drive you nuts. Been there, done that. I have a problem with my R12 system in that cooling comes and goes. I think the issue is liquid flooding the evaporator due to a sticking expansion valve. Not doing anything about it as I am wanting to switch to a more modern GM system with orifice tube.

Definitely will need condenser fan with r134a.

[Sheepdip]

Originally Posted by Davidf

I agree with others. If the high side is low, there are two causes: 1. Low refrigerant or 2. failed Compressor.

I would think that if there was a blockage in the system, the high side would be high.

The sight glass is worthless with R134a.

POA eliminators are junk or annoying at best. A constantly cycling compressor will drive you nuts. Been there, done that. I have a problem with my R12 system in that cooling comes and goes. I think the issue is liquid flooding the evaporator due to a sticking expansion valve. Not doing anything about it as I am wanting to switch to a more modern GM system with orifice tube.

Definitely will need condenser fan with r134a.

Got a second opinion yesterday from a reputable Auto A/C tech....new compressor on the way.