One Rooftop AC Not cooling

[superk]

I have dual rooftop ACs and an intellitec management system. Unfortunately, on this older model there is no amperage draw system. It has 30 amp service labels. I have an onan marquis 5500 generator.

My front AC (Coleman Mach 3) is not blowing cold air. It turns on, and it *sounds* like the compressor kicks in. You can audibly hear the generator momentarily increase its rev when set to COOL, not so much when just set to fan. I see the intellitec Shed the AC for a few minutes when first turned on.

I have searched and found a few nice troubleshooting guides on here which I plan to reference when I go to test the ac in an hour or so.

I have opened the interior panel already and checked the intake filter, while it was dirty, inside the access was spotless, like new. Zero dust. The fins are clean, but warm, not even remotely cold.

The wires do not appear to be damaged, they are practically new.

What would you do next? I am fairly handy and consider myself a do it yourself-er in most cases.

[steved44]

It sounds like a starting capacitor to me. It's under the top cover of the A/C unit. There are some U tube videos on how to change it. It must be drawing too much voltage trying to start, then the intellitec unit sheds it.

[superk]

After a few minutes, the shedding stops and the ac is supposed to now be running. the exact same process happens for the rear ac, which works great and blows cold air. However, after your suggestion I read around about it and have already printed a diagnostic test for it!

I figure at this point I might as well expose its guts and familiarize myself with its workings lol.

[superk]

Ok so, here it is.

http://home.comcast.net/~robmorg/discovery/ecc.pdf

this is my system (or so it seems)

Just for fun, I checked the +12 going to the ac for activation of the compressor. I got no current. So I located the control module above the fridge and slid the test switch to front. The generator went nuts. I think that the AC was drawing wayyyyyyyyy too much power. In the end, it stabilized and the rooftop unit started up. After a few minutes of waiting I checked that same +12v line, and it had current! Still no cold air though.

So now, do I have two problems?

• Is the unit intentionally not powering the compressor? (Perhaps it senses some sort of overload)
• Or, Does the unit have an issue and is just not powering up the compressor due to defect.
• Both?

[loisjop]

Originally Posted by superk

Ok so, here it is.

http://home.comcast.net/~robmorg/discovery/ecc.pdf

this is my system (or so it seems)

Just for fun, I checked the +12 going to the ac for activation of the compressor. I got no current. So I located the control module above the fridge and slid the test switch to front. The generator went nuts. I think that the AC was drawing wayyyyyyyyy too much power. In the end, it stabilized and the rooftop unit started up. After a few minutes of waiting I checked that same +12v line, and it had current! Still no cold air though.

So now, do I have

• Is the unit intentionally not powering the compressor? (Perhaps it senses some sort of overload)
• Or, Does the unit have an issue and is just not powering up the compressor due to defect.
• Both?

Sounds like the compressor has a locked rotor. When you say unit starts I suspect you're hearing just the fan running.

[spyderRV]

I had a PTC hardstart module that was bad, (burned) on my rear AC. Its purpose is to supply additional torque to the compressor for startup assist and it is jumpered across the run capacitor. Sometimes all worked well. Sometimes the PTC would short and kill the generator when the compressor would energize. They are around $11 to replace and I would suggest it be done on general principle on older ACs.

SUPCO Hard Start Kit, AC Compressor SPP6 - G1772574 at Zoro

[TQ60]

Locate a troubleshooting guide for your ac then read it fully.

Way too much current should trip the breaker or the protector on the compressor.

A locked rotor will trip the protector on the compressor.

A start cap usually opens up.

Start cap is cheap and an easy try...

Compressor is fatal to the unit.

Follow the troubleshooting guide as it will step through setup and measurements to isolate the issue.

It means climbing on the roof making measurements of ac or dangerous voltages so plan on having a helper below to flip switches and breakers for you.

A start cap is about 15 bucks so you could pick one up to try but do the troubleshooting first.

A good voltmeter is needed and one with clamp on ammeter best.

[camato5]

Two questions, First is your bus 50 amp or 30 amp service. Second does the AC work if it is the only one running? I thought I had problems with one of my AC units. It turned out to be the 30 amps I was plugged into was not enough to start both AC units. When running the generator OR plugged into 50 amp service they worked fine. Also each worked fine when on 30 amp but only one unit running.

[superk]

Originally Posted by loisjop

Sounds like the compressor has a locked rotor. When you say unit starts I suspect you're hearing just the fan running.

At first, yes, the fan was just running. When the switch was set to test, you can hear the compressor engage (and the generator go NUTS) and after a few seconds, the generator calms down and the fan starts. Whether or not the compressor IS running at this point, will be determined soon. I am going to go get a clamp on meter tonight and test to see if its still running.

Originally Posted by spyderRV

I had a PTC hardstart module that was bad, (burned) on my rear AC. Sometimes the PTC would short and kill the generator when the compressor would energize.

Are you referring to the start-up capacitor? I reviewed the link you provided. It sort of seems as if this is an add-in product?

TQ60, please see quoted message below

Originally Posted by TQ60

Locate a troubleshooting guide for your ac then read it fully.Workin on it!

Way too much current should trip the breaker or the protector on the compressor. That was my thought. I didnt realize there was a protector on the compressor. If this protector trips, is it time-delayed or manual reset?

A locked rotor will trip the protector on the compressor.

A start cap usually opens up. Opens up?

Start cap is cheap and an easy try...

Compressor is fatal to the unit.

Follow the troubleshooting guide as it will step through setup and measurements to isolate the issue.

It means climbing on the roof making measurements of ac or dangerous voltages so plan on having a helper below to flip switches and breakers for you.

A start cap is about 15 bucks so you could pick one up to try but do the troubleshooting first.

A good voltmeter is needed and one with clamp on ammeter best.Going to get the ammeter shortly!

Originally Posted by camato5

Two questions, First is your bus 50 amp or 30 amp service. Second does the AC work if it is the only one running? I thought I had problems with one of my AC units. It turned out to be the 30 amps I was plugged into was not enough to start both AC units. When running the generator OR plugged into 50 amp service they worked fine. Also each worked fine when on 30 amp but only one unit running.

Its 30 amp service. The AC does not work if its the only one running.

[TQ60]

In simple terms a cap acts like a resistor to ac current flow.

It consists of 2 plates seperated by an insulator.

Sometimes they short out wjen the insulator fails and other times the internal connection fails or they dry out and the value falls greatly reacting like an open or not connected circuit.

A shorted one can pop a breaker and open one causes compressor to pull current only on run winding and with no current available to start winding via the cap the compressor draws excessive power and the heat protector kicks in

[spyderRV]

Originally Posted by superk

Are you referring to the start-up capacitor? I reviewed the link you provided. It sort of seems as if this is an add-in product?

Perhaps it is also called a start-up capacitor. It is supposed to give the compressor motor a kick for about a 1/2 second. During this time, the startup current is huge, than it heats up the PTC element and the start-up capacitor's current fades away. Mine would not dis-engage and would load down the generator to the point it would stall. If it looks like an add on it is. I add this device to ALL ac systems I work on. Cheap insurance. I suspect the coaches have these units as standard equipment because the power supply is not "stiff".

[TQ60]

That is called a "hard start".

electric motors for ac power have different configurations to allow them to operate.

3 phase are the simplest but we are dealing with single.

So there is a winding or coil in the motor that makes it turn but it will not make it start turning.

That requires a second winding but it needs to be out of phase with the run winding.

A capacitor shifts the phase of the current flowing through it so a capacitor is added in series with that second winding to start the compressor.

The cap is selected to provide enough current to do the job.

Sizing and exact design are for the motor folks...that is the basics...

Anyway in hot environments the natural pressures are higher requiring more current to get the compressor to start so an additional cap is added to increase the available current.

Thus they are called hard starts.

Long term effects of them added where not really needed is best left to those who do that for a living.

We had them added to many of our comm sites over the years as the compressors aged they needed help...higher heat loads and hot days made their work a lot harder too.

[superk]

Today I went up on the roof. I brought a variety of tools, including a clamp on ammeter. I had my friend Al helping me downstairs with passing of items and flicking switches. At first, the compressor tripped the circuit and was powered down. I then went to look at the caps. I unplugged, discharged, and tested all 3. All 3 tested and visually inspected ok. Plugged them back in, had Al turn it on, and the compressor fired right up. Unfortunately, however, it did NOT produce cold air.

At this point, I think its reasonably safe to say that the coolant has leaked, and there is also potential for complete compressor failure.

Is it worth it to have an HVAC guy hop up on the roof and try to refill this thing? I checked and it is sealed. Ends would need to be cut open, pump applied, and then crimped closed again. I assume there is a tool that does all this without leaking the gas. If the fluid is indeed gone.... there is a leak somewhere right? That could be anywhere in the system.

[spyderRV]

It may not have leaked out the freon. It is possible that the compressor has a failed valve or a loose shaft. Looking around, these units seem to be in the $400 plus price range. It might be more cost effective to just replace the unit.