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Ok, without looking it up somewhere, at what temperature does the fusible plug blow on the refrigerant system for a R-22 carrier heat pump? (50TJ series)
Next question, how in the hell can it get that hot in order to blow out, blowing all the freon into the atmosphere?
And last but not least, what is the saturated pressure of r-22 at that temp??
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If I recall, Fusible plugs really are not for pressure relief due to a fan failure or plugged condenser. A mechanical relief valve is meant for that. A fusible plug is really designed for a unit located in a fire. This would allow the refrigerant to blow off before an excessive amount of pressure could rupture the receiver/system and cause injury or death. Its true that they sometimes fail due to high pressures but originally it was a UL thing for fire, If I recall my facts correctly. I can look at my old Sam's if this discussion goes further.
Rich
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Ive not heard that one but I have seen a lot of Carriers and Bryants with blown fuseable plugs. Always found them on outdoor units with bad cond motors, leaking suction accumulators, leaking evap or condenser coils or screwed up rev valves. Never saw one in a fire yet. Bubba
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Maybe Carrier, (WHICH btw is very possible) has it on their units for low temp release. But I'm very very sure (99.9%) that in refrigeration they mostly are for fire and shipping. Shipping is a big thing as well, a vessel that carries so many pounds of refrigerant must have a relief that if fire hits it the unit will release verses explode.
I've seen them on Carriers too, on the discharge line if I recall, but never found one that leaked.
I'll see if I can even find my books on the subject and if I do I'll look it up. Maybe AC and Refrigeration is different.
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"geoman" wrote:

Rich,
I've seen these plugs ONLY on carrier products, ie Bryant, Carrier, Day & Night, BDP etc. On the older models they're mounted between the accumulator & comp in the copper tubing, the one that blew was located on the top of the accumulator. Rated to blow at 210F. In my case the rev valve is stuck half way between ht & cool. Natchurly I didnt find that out until i evacuated and dropped in a charge. :(
fyi- <most> fusible links (fire dampers, smoke dampers) etc melt at 165F.
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http://en.wikipedia.org/wiki/Cerrobend
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??
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Link to various low melt point alloy and showing actual melting temps.
( Thought wouldn't hurt to divulge...little trade secret...esp beings as someone was suggesting just the other day to fill tubing with sand prior to bending ).
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If there were a fire, would not the mechnical pressure relief open and blow off the pressure before the pressure could build to repture level as well even without a fusible plug??
Mark
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On Wed, 03 Jan 2007 00:46:10 GMT, snipped-for-privacy@gonefishin.net wrote:

Dont actually know the temps but dont care or matter either. Its an old one. They usually blew because the coils or elsewhere were leaking refrigerant. The unit runs hot, the plug melts and out goes the refrigerant. Rretty stupid design but very cheap to make. As usual, Carrier's engineering that says, "Screw the customer. We will protect our compressor. We dont care what it costs the customer to repair." Bubba
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