Pressure safety swtiches?

[Larry2]

Where is the optimum location for high pressure cut-off and low side (loss of charge) switches on a heat pump?

What do these pressures look like on the compressor ports during the reverse-valve shuttle operation?

[LRAC]

Where is the optimum location for high pressure cut-off and low side (loss of charge) switches on a heat pump?

What do these pressures look like on the compressor ports during the reverse-valve shuttle operation?

The switches are always (modern day units normally use thermisters) fitted to the compressor discharge for HP and the main suction of the compressor so you don't get any false readings during the heating cycle.

The pressures should remain the same on the heating stage at the compressor as the manufacturers use restrictors for the suction return,so as not to overheat them.

Don't get confused with the guage ports on the condensing unit you will get completely different readings.

Regards
Lrac

[Larry2]

I was looking for a latching high pressure switch that would require manual reset after a fault. What would I used in this instance?

[LRAC]

Not sure what brands you have over there, but really any manual reset HP switch that you can fit in?

If you wanted to be really clever on the signal side fit a indicator bulb for future diagnosis.

Kind regards
Lrac

[Larry2]

Well, what I did that is causing me issues was to install a Ranco latching limit switch. I've installed the new ZR47K compressor in this system and the replacement didn't have a well for mounting the Klixon over the head. I didn't like that approach with the klixon anyway. I want faults to lock the unit off rather than let it thermal cycle until parts are ground up.

I attached the high side capillary to the compressor liquid line after the muffler and I attached the low side capillary to the suction line, near the compressor. I have it wired so that it opens the compressor power directly rather than by openening the contactor. Sometimes contactors weld shut.

The problem I believe I'm having with my old school Ranco switch is that when the reversing valve shuttles for defrosting mode, the Ranco switch notices a momentary underlimit (or overlimit) pressure. I don't know which; I have to buy new gauges after a mishap. (It was a good excuse to get 1% toys anyway.)

Here's a photo of what I'm up to.

http://i11.tinypic.com/46z5qhh.jpg

[Peter_1]

I know it's an old machien and you haven't made it but I see some things:
the distributor on the left is mounted horizontally :eek:

there's a service valve connection on the discharge line

just before it enters the 4 way-valve, this is for me the best location for your HP cut out. If the 4WV blocks for some reason, then the compressor is protected.
It isn't like you've done it now, on the liquid.

What's that auxilliary relay I see on the bottom, wired together with al the wires?

Is the clixon you wired direct in line with the compressor lines strong enough to switch the current of the compressor?

You've used the shovel on the back of the machine to remove the old compressor? :p

[LRAC]

just before it enters the 4 way-valve, this is for me the best location for your HP cut out. If the 4WV blocks for some reason, then the compressor is protected.
It isn't like you've done it now, on the liquid.

Use the main suction on the compressor and the HP on the feed to the reversing valve as Peter 1 says.

You shouldn't get any fauls tripping.
Lrac

[Larry2]

I notice the distributor is mounted horizontally on both this outdoor unit and on the indoor coil. I see it is done that way in manuals for a number of Lennox units. It's not how sporlan recommends doing business. Sporlan gives the following picture as commentary.

http://www.sporlan.com/dist1.gif

I have the latching HP cut-out switch tee'd off the service valve just before the reversal valve. That is a fitting just below the reversing valve. A small cap tube runs back to the Ranco switch.

I have the latching LP cut-out section of the switch tee'd off the service valve at the suction line to the compressor. That is visible right next to the sight glass which is now happy bright green!

The auxilliary relay with all the wiring is the defrost relay. It cuts off the outdoor fan motor and operates the reversing valve during defrost. It came with that sloppy work from the factory that way. Honest!

The Ranco pressure switch is rated for the full compressor load, so that should be okay.

I didn't think this should false trip, but I believe it is cutting out when the reversing valve is operated. It is an old inventory part I bought cheap, so maybe it's precision is lacking.

[Larry2]

You've used the shovel on the back of the machine to remove the old compressor? :p

Well, no. But I'll admit that as I tipped the top of the compressor back to pull it out feet first from under the pipes. It may have come in contact with the insulation back there. That thing is heavy at arm's length!

The replacement is an inch taller, so a giant shoe horn helped fit the new one in place.

[Peter_1]

Shoe horn,.. i had to look in a dictionary what this was but could imagine that it was that what I thought it was.

[Larry2]

http://www.helpinghand.co.uk/docs/144.jpg


Shoe horn: A specialized tool for fitting big feet into little shoes.

[Peter_1]

Shoe horn: A specialized tool for fitting big feet into little shoes.
Or ..a specialsied tool used by refrigeration techs. :D

[Larry2]

I turned back my safety switch settings and the system has worked flawlessly for a week through various and severe conditions. It was faulting on the low pressure side but I don't know the actual setting of the switch because the pointer is rather crude.

In heating mode, the high side would venture pretty high when temperatures were warmish outside. I've since boosted the indoor blower and pressures are better. I've not seen warm temperatures to have another look.

I'm planning to add a pressure switch for the heating side only that will cycle the outdoor fan motor based on head pressure. I found a Johnson Controls P70CA-3C switch at bargain. (eBay, where else?) I'm thinking of turning off the outdoor fan at 280 PSIG and back on at 240 PSIG. I'm thinking this will only come into play during outdoor temps above 55-60F where this will have minimum effect on operating costs.

I have even more Rube Goldburg stuff in mind for the system to improve comfort and lifespan. I'm looking for comments on this modification before I put the next one out here for discussion.

[NoNickName]

I'd say liquid line for HP switch (lower reading than compressor discharge, but also less pulsation), and suction for LP.
A 320 Psi HP switch will open at 300 under heavy compressor pulsation, that's why I normally use liquid line.

[LRAC]

I'm planning to add a pressure switch for the heating side only that will cycle the outdoor fan motor based on head pressure. I found a Johnson Controls P70CA-3C switch at bargain. (eBay, where else?) I'm thinking of turning off the outdoor fan at 280 PSIG and back on at 240 PSIG.

crrect me iff i'm wrong but i thought that when a system was in heating mode you'd want the outdoor fan running flat out, because you've turned it in to the evaporator.

Lrac