Need advice with a trane GAM

[truck12]

Been having problems with this Trane GAM 3 ton. It a vertical on a stand with a free draw return, has good airflow on the supply side.

I cannot get the suction pressure to go above 115 psi. I don't know the number of the cond unit but it is an trane 042 with a micro coil. I've seen the high side up to 600 on this system and the low side stays below 125.

As suggested by tranes tech line I tested the sensors and stepper motor, they said it was the tube assy (thats what they call the eev, check valve and tubing). They actually called me today and told me I can crimp off the tubing to the check valve since it's not a heat pump, said if the check valve was leaking it could cause the problem I'm having.

I don't have my notes in front of me, so going off memory:
Ambient is 80*
360 psi/115psi
44* suction temp at cond.
40* suction temp at evap.
Input sensor reads 2.59 vdc
Output sensor reads 2.59 vdc (which is 40* IIRC)
Input and output sensors read approx 25,000 ohms (approx 40*)
Supply air is 44*
Return air is 71*
This is a condo, a/h is on the top floor with the cond unit right above on the roof, line set is approx 25'. 3/4, 3/8.

Today I replaced the tube assembly, evacuated, weighed in the nameplate charge of 5 pounds, added 1 more pound to get the suction above freezing.

The before and after readings (above) are exactly the same before and after the repair.

I think it's the stepper motor, tech support didn't think so. The service facts tell you how to check it, but it says it only stays in full open or full closed position for 1.5 minutes, I couldn't get to the roof to check the pressures in that amount of time. Then tech support said I could just test full open or full closed and remove the stepper motor and it will hold position indefinitely. I didn't get a chance to test it like that.

I tested full open I could hear it change pitch. When testing full closed I could hear the compressor making noise and the lineset was vibrating.

What modulates the stepper motor? It seems like it's working but not adjusting it to the right position.
Any ideas?

[mark beiser]

Supply air is 44*
Return air is 71*

If this is true, you have a 27º temperature drop.

You have an airflow problem, not a refrigerant cycle problem.
Any strange behavior of the refrigerant cycle, or its controls, is a result of the airflow problem.

When you say it has "has good airflow on the supply side", is this based on actual measurement of the airflow, or comparing the external static pressure to the blower performance chart?

[truck12]

When you say it has "has good airflow on the supply side", is this based on actual measurement of the airflow, or comparing the external static pressure to the blower performance chart?

According to the tech who was there before me the static pressure is ok.
I also sort of gauged it by seeing how it doesn't try to blow the door off when opening it with it running, it has good airflow out of the grilles. (I know you're not going to like my testing).

I forgot to mention when I was there the first day I recovered the refrigerant, changed a liquid line drier, evac. When I tried weighing in the 5 pound nameplate charge the high side shot up to 600psi at 4 pounds 8 ounces. I don't think thats an airflow problem. (not that an airflow problem doesn't exist).

[mark beiser]

Again, 27º temperature drop = airflow problem.

What speed tap on the blower motor was being used when the other tech got the "ok" static pressure reading?
A 3 ton GAM5 air handler needs to be on high speed to have enough airflow for a 3.5 ton system, and the factory default setting is not high speed.

The micro channel coil in the XB300 has a very limited capacity to store refrigerant stacking up in it.
Even with a short refrigerant line set and a correct refrigerant charge, you can't pump one down.
Even just going a little over on the refrigerant charge, or liquid charging a little to fast, can cause huge spikes in the head pressure.

The EEV in the GAM5 air handler will try very hard to maintain the superheat the control is programed for, so if you have low airflow through the indoor coil, the EEV may be closing far enough to cause to liquid refrigerant to stack in the condenser coil, which can cause bad things to happen with an XB300.

Once you address the airflow problem, you will likely find that your EEV/refrigerant cycle problem will self correct.

[truck12]

I had a feeling there was some refrigerant stacking going on. Thats why I took it out and weighed it in twice.
Fan tap has been on high since I first got there.
This is in a condo, can't get to the duct work. I think I'm going to have to tell my boss not to use these in applications where the duct work is not accessible.

I guess the next step would be to cut the front out of the supply plenum and see what happens.

Thanks for the info.

[SoFlaDave]

GAM5 run less than 400 CFM per ton at anything over .5 static on speed tap 5 @230 V and even less @ 208. Why was the equipment mismatched?

[mark beiser]

Why was the equipment mismatched?

The "3 ton" GAM5 and 3.5 ton XB300 are an ARI rated match.
I'm guessing the GAM5A0B36 air handler was selected because it has a 21" wide cabinet vs the 23.5" wide "3.5 ton" air handler.

I suspect the biggest problem in this case is that the GAM5A0B36 has a smaller version of the X13 blower motor in it than the GAM5A0C42 air handler, and is only capable of marginally adequate airflow for a 3.5 ton system at low static pressures.
I got booted from access to Comfortsite a couple of days ago, or I'd check, but I'm thinking the GAM5A0B36 would be pushing less than 1200 CFM at anything over .3 or .4" WC ESP.

[La Air Man]

Gam5036 can move 1205 cfm at .5 static. The ari rating is at 1335 cfm. At .3 it can move 1301 cfm. I don't think it can do it with tight ductwork.

[mark beiser]

Gam5036 can move 1205 cfm at .5 static. The ari rating is at 1335 cfm. At .3 it can move 1301 cfm. I don't think it can do it with tight ductwork.

Are those numbers factoring in a heat package?

Trane air handler blower performance charts don't include the PD of the heat package, it has to be factored in based on the heat package installed.
If you measure an ESP of .5, and have a heat package with a PD of .1 at the specified airflow, you would look at .6 on the blower performance chart.

IMO, that air handler and a 3.5 ton outdoor unit are a crappy system matchup under most real world conditions, especially with a unit that is intolerant of liquid stacking in the condenser, like the XB300.

[SoFlaDave]

The "3 ton" GAM5 and 3.5 ton XB300 are an ARI rated match.
I'm guessing the GAM5A0B36 air handler was selected because it has a 21" wide cabinet vs the 23.5" wide "3.5 ton" air handler.

I suspect the biggest problem in this case is that the GAM5A0B36 has a smaller version of the X13 blower motor in it than the GAM5A0C42 air handler, and is only capable of marginally adequate airflow for a 3.5 ton system at low static pressures.
I got booted from access to Comfortsite a couple of days ago, or I'd check, but I'm thinking the GAM5A0B36 would be pushing less than 1200 CFM at anything over .3 or .4" WC ESP.

It's struggling for 1300 CFM without a filter at .3 and I imagine that condo duct system is probably well above that. With the heater taken into account. I agree with you Mark, not a great match for this application.

[mark beiser]

It's struggling for 1300 CFM without a filter at .3 and I imagine that condo duct system is probably well above that. With the heater taken into account. I agree with you Mark, not a great match for this application.

Ahh, I see now that the redesign of the heat packages for the Hyperion air handlers was a big improvement, as Trane now calls their PD "negligible"

Still, the chart is for "without filter".
Try moving 1200+ CFM through the typical 20x20x1 pleated filter and the PD through the filter will be >.2

With a pleated filter and a restrictive duct system, the "3.5 ton" system in question is easily moving less than 1100 CFM.

[La Air Man]

IMO, that air handler and a 3.5 ton outdoor unit are a crappy system matchup under most real world conditions, especially with a unit that is intolerant of liquid stacking in the condenser, like the XB300.[/QUOTE]

I'm not a fan of this condenser in general. We installed one and it was very loud and I didn't like the way it had to be charged. What is your thoughts on this unit?

[mark beiser]

What is your thoughts on this unit?

We don't offer them. If I need something with a smaller footprint than an the regular AS/Trane line, I go with a different brand.

[truck12]

I went there today. It was overcharged for one. The last trane tech said to charge it by subcooling even after I reminded him it says on the units charging chart to not charge it by sub cooling. I talked to a different trane tech today who asked me how I charged it last, and when I told him of course I was talked to like a dumbass. I told him the other guy told me to do it like that, thats why I charged it by sub cooling why the F did he tell me to do it like that.

Bunch of f ing a holes these guys are.

This guy said charge it per the charging chart and pay no attention at all to the suction pressure, doesn't matter if it's 80 psi. Ok I did that, still has a 25 degree split. Static pressure supply duct is .07 wc.

I got all readings to intersect on the charging chart. Fan's on high. pressures are 290/118, liq line 88, ambient 85, suction at the a/h is 44

This different tech also asked me why the equipment mismatch, my boss showed me some literature that listed them as a match.

[mark beiser]

Static pressure supply duct is .07 wc.

What speed tap, and did you mean 0.7" wc, or 0.07" wc?
If it is 0.7" wc, which I suspect with that temperature drop, you are only moving around 1100 CFM of air if the blower is on its highest speed, and no filter installed.
That is only 314 cfm/ton, which isn't near enough airflow for the system to work correctly.

If you mean 0.07" wc, I suspect you may not be getting a good reading.


my boss showed me some literature that listed them as a match.

Yes, it is an ARI listed match, and would work well if you had proper airflow.

[truck12]

It's .07 inches water column. Fan on high. inaccessible ductwork, through the grilles I can see seven 8 inch flex drops, a 6" and two fours. But who knows whats in the ceiling........

[mark beiser]

It's .07 inches water column. Fan on high. inaccessible ductwork, through the grilles I can see seven 8 inch flex drops, a 6" and two fours. But who knows whats in the ceiling........

I won't say 0.07" wc is impossible, but on high speed with any sort of duct system connected to it, that would be very highly unlikely.
The temperature drop you are getting through the system would make me doubly suspicious of that reading.

Typically when I encounter a supply static pressure that low, I'll try in another spot and find it is actually much higher, just the first spot was in a part of the supply that was at a lower pressure due to turbulence in the duct.

In my experience, the first foot or so of the front of the supply off an air handler is usually a bad place to take static pressure readings.

Having a pitot tube is handy in situations like that because it gives you more reach into the duct than a static pressure tip.

[truck12]

If I was running the show here this wouldn't be an issue. I'm just the unfortunate ******* that gets to polish the turds, and explain to the customers why it still smells like a piece of ****.

[truck12]

and apparently it doesn't smell that bad so it's going to stay as is until the customer calls back. Which may or may not happen. Hopefully not because I'm out of turd polish.