AC help needed

[bigdave720]

I got my previous low voltage problem taken care of. Holding in the 118 to 120 range now. New problem is my 14 year old Coleman Mach 15k ac.

I've had both sets of coils cleaned. New gasket installed due to small leak. Air coming from the vents stays right around 53ish degrees until outside temps start getting into the mid to upper 80's. At that point vent temps start increasing into the mid 60's. Once outside temps get into the 90's vent temps get into the 70's. Now I realize that is fairly normal. Problem is that once outside temps get into the 90's ac starts tripping the 20 amp breaker it runs on. Basically I have to shut it down completely from around noon until around 6pm daily with the current heatwave we've been experiencing for the past couple of weeks. I've replaced the breaker but that didn't help. What do I check now or am I to the point of needing to spring for a new ac?

[bigdave720]

You must have missed the next sentence. "Apparently the compressor never comes on." Since there is a fan AND a compressor I assumed it would be easy to understand but I apologize for not spelling it out clearer.

I was able to get someone to try connecting the thermister for me today and VOILA! Works like a brand new ac now except it only blows straight down until I can get someone to button it up for me.

[kellertx5er]

Runs "great" but never blows cold?

[bigdave720]

Well, I bought a new ac. Got brothers to change it out for me. Now they got it wired up just like the old one was (and the next to worthless instructions call for) and it runs great except it never blows cold. Apparently the compressor never comes on. The guy at the shop where I bought the ac said my old thermostat should be fine but do you think it is the problem? Currently they have the electrical box hanging down waiting for it to test good before buttoning it up so the thermistor is plugged in but not attached to the compressor coil. Any chance this could be the problem? I can't get to it to test it so I'm trying to get an idea what they will need to do tomorrow. Help?

[bigdave720]

Thanks for such detailed info Ken. I'm only about 3 hours from AdventureRv so I've talked then into letting me pick it up instead of shipping, saving $125 minus the sales tax. So hopefully we're doing this Monday for a cool Tuesday.

[TXiceman]

It is an easy swap. The hard part is getting the new unit on the roof.

Place some plywood up top to work from.

Remove the interior cover and remove the 4 hold-down bolts,
Disconnect the A/C unit at the breaker first. Then disconnect the wires at the unit.
Next on the roof roll the unit onto its side and then get it off the roof.
Get the new unit on the roof.
Lean the unit on one side and install the new gasket on the bottom of the new unit.
Clean the gasket area on the roof.
DO NOT use any caulk on the gaskets.
Place the unit over the hole.
Inside now, and center and square up the unit to the opening.
Install the retaining plate and the 4 bolts.
Tighten the 4 bolts evenly and compress the gasket to 1/2 of its original thickness.
Reconnect the power wires to the new unit,
Check the the baffle between the inlet and outlet air is sealed properly.
Reinstall the interior cover and trim.
Turn on the breaker and then turn on the new A/C unit.

The 20 amp breaker and wire is suitable for the 15000 BTUH unit.

Ken

[bigdave720]

Nope. Current ac is a Coleman Mach.

[SALEM1]

I assume your current AC is a Dometic Brisk Air II. Everything between the 13K and 15K is the same except that the 15K weighs 2 extra pounds (74 vs 72). Should be plug & play all the way.

[bigdave720]

Thanks for all the words of wisdom guys. It seems the best way to spend my money is to just buy a new ac. It turns out I was told wrong. There's nothing inside that I can get to that specifies 13.5k or 15k and I was told it was 15k. But, when I had my brother get on top for me he discovered it was actually a 13.5 unit. So..... new question is if I upgrade to a 15k is this just an easy swap or do I need new wiring or anything? Is the 20amp breaker right or does it need 30amps? Thanks.

[christopherglen]

At 14 years old, it is really long in the teeth, a newer unit will likely work better outside of noon to 6 pm, and definitely better between.

[SALEM1]

When using the A/C in very hot weather, the A/C 20 amp breaker gets hot (normal) and the main 30 amp breaker also gets hot. Since the A/C breaker is installed adjacent to the 30 amp breaker, I have experienced that the temperature is compounded and one or the other trips not because of current load but because of temperature. My solution has been to relocate the A/C breaker a couple of positions down so that it is not next to the 30 amp main. To make it easy I just swap breakers with the microwave. Again, this will prevent nuisance trips due to temperature not load.

[Fulltimer50]

golf_bears wrote:
If I understand your problem based on the info you've provided you are running a 15k AC unit on a 20 amp circuit. At high outside temperatures the AC unit keeps running and trips your 20 amp breaker.

A 15k AC unit needs about 22 amps to kick start it. So if it runs almost continuously when outside air is at 90 degrees it makes sense that the breakers are overloaded and too hot.

You need that AC unit running on a 30 amp circuit.

I dont know about your numbers but ACs run on 20 amp circuits. As are my two and every one I have ever had (5-6).

[C_Schomer]

You need to use an amp clamp/meter and verify the current draw and voltage and go from there. The breaker needs to be HACR rated... heating/AC/refrigerating. I also use thermocouples to check for proper refrigerant flow/temps. It's really easy to check subcooling and superheat that way and see if the filter/strainer or cap tube is restricted. Your symptoms would make me look for a restriction or dragging fan motor... after cleaning the coils. I wish I had a dollar for every drier I've replaced on old systems and made them work like new again! I've added a SUP hard start to a RV AC that had a high amp compressor but that only made it last another 1 - 1 1/2 months. That old AC might not be worth spending very much on it. Craig

[golf_bears]

If I understand your problem based on the info you've provided you are running a 15k AC unit on a 20 amp circuit. At high outside temperatures the AC unit keeps running and trips your 20 amp breaker.

A 15k AC unit needs about 22 amps to kick start it. So if it runs almost continuously when outside air is at 90 degrees it makes sense that the breakers are overloaded and too hot.

You need that AC unit running on a 30 amp circuit.

[2oldman]

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