# High pressure switch cutout limit



## HVACDave (Oct 16, 2007)

As a rule of thumb you would take your highest expected condensing temp and add 30F change to Psi for the refrigerant you are working with and you should be close.

Eg. 105-110F expected condensing temp +30 = 135-140F for 410a= approx. 510 PSI, so 525-550 PSI should be about right.

135-140F for R22= 316-335 so many set at 325-350 PSI

Depends on where you are as to what you would expect highest normal condensing temp to be. Where I am 90-100F would be very hot day, where you are may be average summer temp. Newer condensers work on approx. 15-20F condensing temp above ambient, older units approx. 30F above ambient. Depends how clean outdoor coil is as well.
Keep in mind just rule of thumb info. Specific equipment may differ depending on seer rating and all other factors that work into loading etc.


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## Doc Holliday (Mar 12, 2011)

I was working on five rtu's the other day, 4 and 5 ton 410As, and one was tripping at 450. 

I've seen residential 410a go to 500+ before tripping. 

What's yours tripping at?


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## beenthere (Oct 11, 2008)

a.man1302 said:


> What is the average pressure a high pressure switch would open at for a 4ton rooftop package unit with r410a?


Condensing temp used for rating efficiency is 105°F. So most OEMs will have a high pressure switch trip of 425 or more.


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## a.man1302 (May 12, 2014)

Doc Holliday said:


> I was working on five rtu's the other day, 4 and 5 ton 410As, and one was tripping at 450.
> 
> I've seen residential 410a go to 500+ before tripping.
> 
> What's yours tripping at?


 Well the unit in question had a high side pressure of about 425... I'm in Southern CA so the temps are normally over 100 during the summer. This unit has been is 2 years old and the owner has been having this problem since last year... It intermittently stops cooling.


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## a.man1302 (May 12, 2014)

Update: I bypassed the high pressure switch and the unit has not had any problems since... Spoke with owner about replacing switch with one with a slightly higher limit... Kept gauges on for about an hour and temp/pressure don't fluctuate so I'm confident it is the switch. Originally I thought it may be the condenser fan motor failing but I wasn't sure which is why I bypassed the high pressure switch.


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## beenthere (Oct 11, 2008)

Put a 525 on it. That leaves room for hotter then normal days.


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## a.man1302 (May 12, 2014)

Thanks for the responses.


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## Rob Coomer (Jul 18, 2017)

Hi Guys, I live in the UK and work on a lot of rooftop units and larger chillers. All the units with R410A have fixed hp switches and trip at between 40 and 45bar (580 - 652psi). These units are air cooled units.


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